Why does the idle speed fluctuate? We'll help you quickly find the reason
There are a large number of reasons why idle speed floats, this makes finding the source more difficult. The problem with floating idle can occur in carburetor or injection engines, and the search for the cause may differ significantly.
Today I bring to your attention the most common causes of floating idle, ways to find and eliminate them.
Idle speed fluctuates - possible causes
On injection engines, fuel injection is controlled by the ECU (electronic control unit “computer”, “brains”).
In the event of a malfunction of any sensor that is responsible, for example, for metered air supply (MAF), this may cause a “misunderstanding” between the ECU and the sensor, resulting in malfunctions and disturbances in engine operation, which often manifest themselves as floating idle speed .
Quite often the idle speed fluctuates due to:
- Problems in the operation of the mass air flow sensor;
- Faulty idle air controller (IAC);
- Air leakage into the intake system;
- EGR sensor;
- Clogged air filter;
- Faulty spark plugs;
- Problems with wiring (power).
We are looking for reasons why idle speed fluctuates
First you need to try to understand what caused the unstable idle. The first step is usually to check the IAC. This sensor is mounted on the throttle body, near the throttle position sensor (TPS). To check this sensor, use a multimeter.
The principle is approximately the following:
The ignition is turned on, the block with wires is disconnected from the sensor, then the resistance between the contacts is measured: AB, CD IAC.
The resistance of a working sensor should fluctuate in the range from 40 to 80 Ohms; the presence of deviations indicates a malfunction of the idle air regulator. If the resistance is normal, check it also between contacts: AD and BC.
For this measurement, the device should display infinity or an open circuit. If a malfunction is detected, replace the IAC.
The second sensor on which “suspicion” falls is the mass air flow sensor (MAF or flow meter). Floating idle values can often be caused by the flow meter. In order to confirm or refute the version of a faulty mass air flow sensor, it must be checked. Read: How to check the mass air flow sensor at home.
The EGR valve is an exhaust gas recirculation system sensor.
The task of this system is to direct part of the exhaust gases back into the combustion chamber of the cylinders, thereby achieving the most complete combustion of fuel and reducing the emission of harmful gases into the atmosphere.
This system is characterized by relative simplicity and at the same time great capriciousness. The EGR valve is located in the intake manifold and connected to the exhaust manifold. In order to avoid problems, it is recommended to occasionally clean the valve seat, as well as its seating area.
Cleaning is carried out using a special liquid for cleaning carburetors, and care must be taken that the liquid does not get on the valve diaphragm. If the EGR system has a solenoid, clean the vacuum channel filter located in it.
The reasons for floating speed are often simple damage to high-voltage wires. In order to check high-voltage wires, you need to perform a simple check described in this article.
Unstable idle speed in carburetor engines can occur as a result of the following malfunctions:
- Incorrectly adjusted carburetor or malfunction;
- Air leak;
- Problems with the idle air solenoid valve or wiring;
- Irregularities in the ignition system;
- Clogged air filter.
Most often, the reason lies in an incorrectly adjusted idle speed of the carburetor. The problem is solved by adjusting the carburetor using two adjusting screws - “quantity” and “fuel quality”.
A malfunction of the idle air solenoid valve is the second most popular cause of floating idle speed. To check the valve, you need to remove the power wire from it.
Turn on the ignition and touch the contact wire on the valve, as a result you will hear a distinct click. If there is none, touch the contact with the wire that is connected to the “+” terminal of the battery. If after this you do not hear a click, the valve is faulty.
If you hear a click, but the suspicion has not disappeared, take it out and clean its jet.
The problem when the idle speed is floating may also be due to contamination of the carburetor (clogged jets or channels). In this case, use carburetor cleaning fluid and then blow it out with compressed air. Details on how to clean the carburetor are written here.
If you suspect the ignition system, you need to check the distributor, spark plugs, and high-voltage wires.
http://avtopulsar.ru/
Source: http://avtopulsar.ru/pochemu-plavayut-xolostye-oboroty-pomozhem-bystro-najti-prichinu/
When the engine heats up, the speed fluctuates: possible causes, diagnostics, repairs
A fairly common malfunction that is typical of gasoline injection and carburetor internal combustion engines, as well as diesel engines, is the problem of floating engine speed.
It is important to understand that if the engine speed is floating at idle or under load, this indicates the need for comprehensive diagnostics in order to identify and eliminate faults.
In this article we will talk about why the speed floats, what danger this problem can pose to the power unit, and also for what reasons the speed floats when hot.
Engine speed fluctuates: symptoms and main causes
First of all, the tachometer helps to notice floating speed. Most often, the floating speed appears at idle. Normally, even on a slightly warmed-up engine, the tachometer needle should remain stable at about 800 rpm while idling.
The only exception is the warm-up speed XX, when the ECU on injection engines itself raises the speed to 1000-1100 rpm. In this case, after the engine temperature rises slightly, the control unit will lower the idle speed to the desired level of 750-800 rpm.
If engine malfunctions occur, then the tachometer needle may drop significantly, then rise again (the speed jumps, for example, from 500 rpm to 800 rpm, from 800 to 1500 and then drops again to 500 rpm).
Also, jumps in speed can be observed if you increase the load on the engine (press the brake pedal, turn the steering wheel in a car with hydraulic booster, turn on the air conditioning or climate control, etc.).
The revolutions may also fluctuate while driving in transition modes.
In this case, without additional load, the engine can keep the speed stable at idle, but as soon as the load appears, the speed drops, and the engine almost or completely stalls.
By the way, if the car does not have a tachometer, floating speed can be determined by ear by the sound of the engine, since the noise of the internal combustion engine under the same load constantly becomes stronger and weaker, vibrations also change in intensity.
The driver may also notice a significant increase in fuel consumption, the engine response changes when exiting transient modes, jerks and dips may occur during acceleration, etc.
Common causes of floating revolutions
So, we figured out the main symptoms. Now let's move on to the reasons. Let us immediately note that floating idle speed is often a problem with injection engines. The fact is that a complex ECM system is responsible for idling in this case.
This system assumes the presence of a controller, sensors and actuators. The control unit receives signals from sensors and transmits commands to actuators (for example, IAC), maintaining stable engine speeds at idle and other modes, regardless of the load on the internal combustion engine.
However, any failures that are associated with the supply of air, fuel, a violation of the composition of the working fuel-air mixture or its ignition, as well as various mechanical breakdowns will lead to floating speed.
It turns out that you should start checking with the throttle assembly, sensors and actuators. The ignition system, idle air regulator, mass air flow sensor also need diagnostics; it is necessary to assess the condition of the fuel and air filters, injection nozzles, etc.
- As a rule, in practice, the idle air regulator causes a lot of problems for drivers. In fact, this is a stepper motor that has a conical locking needle. When the throttle valve is closed, air bypasses the valve through a channel that is closed by the needle.
If malfunctions occur in the operation of the device, the ECU is not able to correctly “select” the mixture composition at idle, as a result, the speed floats.
- The mass air flow sensor also deserves special attention. During operation, the air flow sensor may become dirty or break down.
One way or another, the ECU does not receive correct data on air flow, which leads to disruption of mixture formation and jumps in engine speed.
- Often, a floating engine speed can be associated with severe contamination of the throttle valve itself or mechanical breakdowns of the throttle, damage, or deformation. The damper may jam and not close completely.
To prevent such complications, it is necessary to periodically clean the throttle from dirt, and on many cars, additional training of the throttle is required after cleaning.
- During diagnostics, you should also check the crankcase ventilation valves. Normally, crankcase gases are redirected to the intake, where they are mixed with air and fuel, after which they are burned in the cylinders.
On engines with mileage, a lot of crankcase gases accumulate due to natural wear and tear of the CPG. An excessive amount of such gases leads to a violation of the composition of the mixture if the crankcase ventilation valve jams. This is also a common reason why engine speed fluctuates.
- By the way, if you touch on carburetor engines, the speed on the carburetor floats, usually due to the settings and adjustments of this device being messed up. Also, one should not exclude the possibility of a breakdown of the carburetor solenoid valve or clogging of the idle jet.
Let’s also add that if the speed of a diesel engine fluctuates, this is often caused by rust on the fuel injection pump blades. Corrosion occurs due to the presence of water in diesel fuel.
Tips and tricks
Let's look at how you can eliminate some of the malfunctions that lead to floating and speed jumps, and do it yourself.
- As mentioned above, the leakage of excess air can cause surges. To exclude or confirm the possibility of supplying such air, you need to check the tightness of the air supply system to the intake. You can remove the air hose and feed it air from a compressor or pump by placing the hose in a container of water. This method helps to identify cracks.
- As for the idle air control, you need to measure the resistance with a multimeter. If the resistance is between 40 and 80 ohms, this means that the device is not working.
- Also, as part of diagnostic procedures, in some cases it is necessary to clean the crankcase ventilation valve. The valve must be removed and washed with carburetor cleaning fluid or kerosene. This approach will remove deposits from the valve.
We also recommend reading the article about why the speed fluctuates on a cold engine. From this article you will learn about the reasons for jumps and floating speed on a cold engine, as well as ways to determine the cause and eliminate this malfunction.
- As for the ECM sensors, in this case it is not advisable to try to repair such elements. For example, if the mass air flow sensor is faulty, it is better to immediately replace it with a new one.
- It is better to trust specialists to flush the throttle valve without proper experience, especially if such flushing is necessary with the removal of the valve. If we talk about the method of flushing the throttle without removing it, you can do the procedure yourself. The hoses are disconnected from the valve, then a cleaning aerosol is injected into the throttle.
The main thing is to disconnect the electrical contacts from the throttle valve. Let us add that on many cars where the damper was heavily dirty, you then need to additionally set the correct opening gap of the damper or “teach” the throttle using the appropriate equipment.
- On a car with a carburetor, you need to adjust the idle speed by setting it with the quality and quantity screws on the carburetor. The idle jet may also need to be cleaned. To do this, it is often enough to inject a carburetor cleaning aerosol and then blow it with compressed air.
Let’s also add that to remove rust from the fuel injection pump, you can use special cleaners that are poured into the fuel tank. Also, some sources mention a method where a little motor oil is added to the fuel (about 200 ml per full tank).
According to drivers, this helps protect the pump from corrosion and is a preventative measure. At the same time, we note that this method is suitable for construction equipment and it is highly not recommended to practice such solutions on modern diesel internal combustion engines.
Let's sum it up
As you can see, there are many reasons why engine speed fluctuates and fluctuates. Moreover, in some cases, unstable speeds can appear both on a cold and hot engine, in idle mode, in transient modes, under load, etc.
We also recommend reading the article about why the engine stalls at idle. From this article you will learn about the main reasons why the engine stops idling, as well as methods for diagnosing and repairing this problem.
It is important to understand that if the engine speed fluctuates (hot, cold or constantly), this malfunction is quite serious and requires a quick solution to the problem.
Otherwise, further operation of the engine may lead to breakdowns of the power unit and its expensive repairs.
Source: http://KrutiMotor.ru/plvayut-oboroty-posle-progreva-dvigatelya-prichiny/
Auto engine speed sensor
When car enthusiasts have certain problems with the engine, they begin to wonder which sensor is responsible for engine speed, since the first suspicion often falls on these devices.
However, this is not always the case, because the speed can “float” for various reasons. It is best to first make sure that there are no other damage, and check the meters afterwards. One way or another, if you want to locate the sensor you need, you need to know what it looks like and where to look for it.
Basic Concepts
This power unit meter is the most important element of the car, without which the interaction of many systems is essential, because it helps ensure the correct functioning of the entire car as a whole.
The car's electronic control unit processes the special signals that this meter sends to find out:
- amount of fuel injected at the moment;
- injection moment;
- time required to activate the adsorber valve;
- ignition timing (for gasoline engines);
- the angle of rotation of the camshaft during operation of the system to change the phases of the gas distribution mechanism.
To determine the performance of the meter, you need to know its location.
Location
The speed sensor, or induction meter, is usually located above the vehicle's marker disc.
The disk, in turn, may be located:
- on the flywheel;
- on the crankshaft inside the cylinder block - this happens with brands Ford, Opel, etc.;
- in front of the engine compartment on the crankshaft, together with the drive pulley for additional units (Jaguar, BMW, VAZ, etc.).
It is best when the marker teeth of the flywheel are intended only for measuring engine speed. It’s a little worse if the starter teeth are marker teeth: this feature is present in Audi and Volvo cars.
A slight curvature of a flywheel tooth or a small chip present on it can often cause a malfunction of the ignition system, due to which the power unit cannot operate at high speeds. In this case, chaotic sparking often occurs because the control unit incorrectly determines the number of teeth.
Important Features
It should be noted that on some cars the rotation speed sensor replaces the Hall meter: this device can transmit to the main control unit not only a signal about the valve timing, but also engine speed. If this is exactly the situation you have, then you can find the device near the camshaft.
If the crankshaft speed meter fails, you will not be able to start your car: after a thorough check of the ignition and fuel supply system, during which no significant deviations are found, it is recommended to check the performance of the speed sensor.
Conclusion
If you have no doubts about the operability of all the most important systems of the car, it is recommended to ask yourself which sensor is responsible for engine speed. To find the cause quickly and more accurately, it is recommended to diagnose the car in a timely manner, but do not forget that in some cases you can do without it.
Source: http://AvtoTehnar.ru/datchik-oborotov-dvigatelya-avto/
Signs and symptoms of faulty car sensors
Good day, dear readers, in this article we will analyze many reasons, but mainly the symptoms of malfunctioning car sensors. Remember that before you go to a service station and panic, you should spend a little time and try to find the cause of the problem yourself and save money.
Signs of a malfunction of the TPS sensor:
— high speeds are possible at idle, this is the most characteristic sign; — a noticeable decrease in engine power and deterioration in throttle response; — when pressing the accelerator there are jerks, dips and twitches; — floating speed at idle; — when changing gears, the engine turns off spontaneously; — overheating is possible; - detonation.
(personally, my symptoms were high speeds, inability to brake the engine, jerking, decreased power and, accordingly, increased gas consumption).
The photo shows very worn tracks
The reasons for the malfunction of the TPS sensor can be: - oxidation of the contacts - you can help in this case, you need to take a special WD liquid and clean all the contacts in the block and under the cover with a cotton swab; — worn sensor substrates if their design included sputtering of a resistive layer; - the moving contact fails - some tip of this contact may break, then scoring will form and other tips will also fail;
- the throttle valve does not close completely at idle - in this case, you can slightly file the sensor seats and the throttle valve should close.
The emergency sensor rarely fails, but the average car owner will not be able to diagnose its failure, and some do not know where the sensor is located. The sensor is located opposite the throttle valve.
The check error does not always appear.
Article about TPS repair.
Signs of a malfunctioning idle air valve:
— unstable engine speed at idle; — spontaneous increase or decrease in engine speed; — stopping the engine when the gear is switched off; — no increased speed when starting a cold engine;
— reduction in engine idle speed when the load is turned on (headlights, stove, etc.).
The idle control valve will not be able to function normally in this state.
The check error does not always appear.
The best prevention for the idle air valve is to periodically remove and clean the idle air valve, usually done in the fall and spring. The valve is located near the throttle valve.
Signs of a malfunction of the mass air flow sensor:
Signs of a malfunction of the air flow sensor or absolute pressure in the intake are characterized by: - Up to 70 degrees the car works more or less well, after 70 an unstable idle begins; — Failures during acceleration and adjustments; — The car sometimes stalls at idle when the gas pedal is sharply pressed; — Increased consumption; — Unpleasant exhaust smell;
— Popping noises in the muffler during operation and sometimes popping noises in the intake manifold. (incorrect ignition timing due to faulty sensor)
The air flow sensor is very sensitive and it is not recommended to clean it yourself; the more often you change the filter, the longer it will last you.
The check error only appears when the air flow sensor has stopped working completely, and it can give incorrect readings for a long time.
You can check the air flow sensor or mass air flow sensor by having a multimeter or diagnostic scanner on hand.
Signs of a malfunctioning speed sensor:
— the speedometer does not work or gives incorrect readings; — unstable idling; — increased fuel consumption; - the engine stops developing full power. — the fuel gauge needle reacts almost instantly to fluctuations in the fuel level in the tank, because
the computer thinks that the car is not moving and “smoothes” the sensor readings less; — the odometer does not show mileage; sensor in the automatic transmission - when changing speed, the automatic transmission resets itself to neutral, or switches spontaneously in an illogical manner; — the car stops responding to the gas pedal and coasts;
— in city driving, when picking up speed, the box sharply increases speed and does not accelerate, does not react to other modes 2 and 1. It seems to only drive at speed 1 but does not slow down with the engine.
The principle of operation of the speed sensor on all cars is the same and it is quite possible to restore it yourself; let’s look at the example of repairing a Nissan cefiro speed sensor. The speed sensor is located, in most cases, on the automatic transmission side.
Signs and causes of a malfunctioning knock sensor:
— It rarely fails. Before the sensor breaks, something is more likely to happen to its wiring. Perhaps something happened to them if, at speeds exceeding 3000, the engine’s sensitivity to how high-quality fuel is poured into it increases. If the fuel turns out to be of poor quality, finger knocking will occur.
- symptoms of incorrect ignition timing. Anyone who has driven a car with a manual engine control system knows what I'm talking about.
If you only shift the OZ a few degrees to the early or late side, the engine will either lose its dynamics, as if you were driving with a handbrake, or it will begin to detonate—ringing at light loads or “shooting” into the exhaust system.
Everything depends on the detonation resistance of the fuel poured in and the level of pressure at which your engine operates.
For example (from experience), I came across an Audi with a V-engine with two knock sensors, which flatly refused to develop full power. The engine was gaining momentum very sluggishly, and Pavlodar specialists pointed to a clogged fuel system.
However, when tested on the bench, the injectors sprayed fuel perfectly, and the pressure gauge showed the reference pressure value in the rail. But still, when measuring the OZ with a strobe, it turned out that it was shifted by more than 10 degrees from the normal value, which is described in the manual.
The reason for this was one of the two knock sensors on the second engine block.
Another interesting case involving a faulty knock sensor was with a Subaru engine. When purchased, the car, like the Audi described above, did not develop full power.
At the same time, the engine ran very smoothly, the fuel system (injectors, gas tank) was absolutely clean and there were no signs of any malfunctions at all. However, the owner of the car complained that he couldn’t overtake a regular fuel-injected 10-cylinder.
Based on our experience with Audi, we checked the knock sensor on this engine, but the sensor turned out to be very “alive”. Resistance is 540 kOhm, as required by the specification. The DD reacted quickly to tapping - 30-40 mV.
The reason was not found soon. On several American sites I found owners of exactly the same cars who also complained about the terrible engine dynamics.
But smart Americans quickly realized what was going on and bypassed the knock sensor circuit with a capacitor, and there were those who didn’t really want to tinker with electronics and preferred a pad made of a piece of rubber, which was placed under the sensor.
As a result, the sensitivity of the DD was reduced and the appearance of small vibrations in the motor was completely ignored. Thus, after just a few kilometers the car became playful and dynamic.
The check error does not always appear.
Signs of a malfunctioning coolant temperature sensor:
— The electronic control system sets the engine temperature suitable for starting to a value of zero degrees Celsius and the corresponding command is sent to the additional air regulator.
If the temperature sensor malfunctions, the proportions of air and gasoline in the mixture will be far from optimal, which will make it difficult to start the engine in low temperatures.
After the engine manages to start, after two minutes, the electronic control unit will decide that the coolant temperature has risen to 80 degrees.
For this reason, you will have to use the gas pedal not only when starting, but also when warming up the engine. The same malfunction will cause problems in hot weather.
When the engine heats up to a temperature close to the maximum permissible, the control unit will assume that the antifreeze temperature is normal and will not take measures to adjust the ignition timing. There will be a loss of power and engine detonation will occur.
— idle speed is below normal. — incorrect operation of the car fans, they turn on when the engine is cold and do not turn on when required, as a result of which the temperature increases.
— the appearance of dark smoke from the exhaust pipe.
On most cars there are 2 coolant temperature sensors, data from the first goes to the instrument panel, and turning the radiator fan on and off depends on the data from the second sensor.
The error does not always appear.
Signs of a malfunctioning camshaft position sensor:
— the gearbox is blocked in one gear, usually the first, restarting the engine can solve the problem; — the car moves jerkily; — the car experiences difficulty accelerating after 60 km/h. — the engine stalls periodically, this especially often happens at idle speed; — popping noises in the exhaust gas system are possible;
— the spark disappears, the engine cannot be started.
Signs of a malfunctioning crankshaft position sensor:
— during intense acceleration, detonation appears; — unstable idle speed; — the car’s speed rises or falls on its own;
— I can’t start the engine.
Signs of a faulty ignition coil:
— It breaks down quite often. Symptoms include power loss, decreased overall engine power, rough idle, rough acceleration, and even two cylinders shutting off.
If the distance to the service station is several kilometers, and it is possible to get to it, then turn off the corresponding injectors.
Otherwise, gasoline, injected by injectors into non-working cylinders, and oil will be washed off from the disabled cylinders, after which it will flow into the crankcase.
You can check by turning off the ignition coils one by one and when you come across a faulty coil, the engine operation will not change.
Signs of a generator malfunction:
— When the engine is running, the battery discharge warning lamp flashes (or lights up continuously); — Discharge or overcharging (boiling) of the battery; — Dim car headlights, a rattling or quiet sound signal when the engine is running; — Significant change in headlight brightness with increasing speed. This may be acceptable when increasing the speed (re-throttle) from idle, but the headlights, having lit up brightly, should not increase their brightness any further, remaining at the same intensity;
— Extraneous sounds (howling, squeaking) coming from the generator.
Source: https://autozona54.ru/statyi/polezno-znat/priznaki-i-simptomy-neispravnosti-da.php
VAZ sensors - the main sensors on injection VAZ cars
So, dear visitors, today we will tell you about the main sensors on the VAZ.
Since the operating principle of injection engines in the AvtoVAZ line is the same, in principle we have put together a manual on the sensors that are installed on injection VAZs by the manufacturer, and have prepared a brief description of the operating principles and purpose of each of the sensors below.
Indeed, in essence, the very principle of operation of an injection engine is the interconnected work of the “brains” (ECU) and various kinds of sensors; there is a constant exchange of information between them and, depending on the totality of certain indicators of the sensors, the controller prepares the mixture and ensures stable and correct operation of the engine.
So let's start with the crankshaft position sensor DPKV . (pictured above)
Without this extremely important sensor and if it malfunctions, the car simply will not start.
DPKV generates signals to the ECU using a special toothed disk, on which, upon careful examination, you can see what appears to be a “missing” tooth; this disk is installed directly on the crankshaft. DPKV on VAZs is located on the oil pump cover.
The sensor is quite reliable and its failure is rare. But nevertheless, if it fails, you will have problems. We recommend carrying it with you in the glove compartment just in case.
Let's move on. Another important sensor is the throttle position sensor TPS .
This sensor works in conjunction with the idle air control valve to determine how open the throttle valve is. If this sensor begins to fail or fails altogether, then we will not see a stable idle and the engine speed will live its own life. Dips may also be felt, the engine will pull jerkily, in general it is not pleasant.
Now we are presented with a phase sensor, or camshaft position sensor DPRV .
It determines the position of the camshaft. Not used on 8-valve engines of early injection VAZs. Participates in the formation of phased injection, that is, the desired injector of a particular cylinder works at the right time.
If the sensor is faulty, then the system works as if it were not there, and fuel is supplied in pairs-parallel mode, which leads to excessive consumption of gasoline with all that it entails.
That is, you can drive, but it is not necessary; it is better to replace the faulty sensor.
Now let's look at the DD Knock Sensor .
It is installed directly on the engine block between the third and second cylinders. There are two types - resonant and broadband. These two types of sensors are not interchangeable.
It corresponds entirely to its name, monitors engine detonation and, depending on the presence and strength of detonation, helps the “brains” adjust the ignition timing (ignition timing).
If the sensor fails, the engine will slow down and gasoline consumption will increase.
Now let’s move on to a sensor that is familiar to all of us, which also played an important role in carburetor cars - this is the DTOZh coolant temperature sensor .
It controls the coolant temperature, transmits information about this to the ECU, which, in addition to turning the radiator fan on and off, uses it for a host of needs, from operating the adsorber valve to adjusting the speed on a cold engine
Now the next sensor is the speed sensor.
It generates pulses depending on the speed of the vehicle, is installed on the gearbox; all injection VAZs use exclusively six-pulse DCs. In addition to the speedometer and odometer readings, it also affects the mixture formation, so do not neglect its serviceability.
The next sensor in our manual is the mass air flow sensor DMRV .
The sensor plays a significant role in the operation of the engine, so very often the symptoms of its incorrect operation are a floating idle, uneven engine operation at low speeds, deterioration of traction, in general, not very pleasant.
It is located immediately after the air filter and controls the amount of air taken from outside. Quite an expensive sensor.
Read this article about how to check its functionality and try to restore it in case of a malfunction.
Lambda probe or oxygen concentration sensor
determines the amount of oxygen in exhaust gases and takes an active part in engine mixture formation.
On Euro-2 there is 1 lambda installed, on Euro-3 there are already two, but the second one does not participate in mixture formation and simply performs a controlling function.
With a mileage of 80-100 thousand kilometers, it may well fail or become clogged and give incorrect readings; therefore, deterioration in engine dynamics and excessive fuel consumption are guaranteed.
Well, for starters, one of the most capricious sensors is the Idle Air Controller (IAC)
This sensor is responsible for stable idling. Allows air into the engine at idle speed, bypassing the TPS.
It is on this that the stable idle speed at the required speed primarily depends; it very often fails, and there is also a very high percentage of defects among new sensors.
Well, that’s all in a nutshell, we hope that a short educational program on the sensors used on injection VAZs helped you get a picture of the operation of an injection engine. Good luck to everyone on the roads.
Source: http://www.vazdriver.ru/datchiki_vaz_osnovnye_datchiki_na_inzhektornyh_avtomobilyah_vaz.html
For what reasons does the engine speed fluctuate?
Many car enthusiasts know that the engine is the “heart” of the car. And, of course, problems occur from time to time in the operation of such a valuable device. And people recognize this by the characteristic sounds - the revolutions.
If the engine speed starts to fluctuate, this means that there is something wrong with the device. And in this way it just lets you know. In our article we will talk about what problems may arise with the motor in such situations, as well as how they can be solved.
Why do floating speeds occur?
You can easily understand that the engine has problems with speed. To do this you need to look at the tachometer. If the engine idle was optimal, then the needle on the device would remain at the same level. But when problems arise, the needle behaves differently: it jumps in different directions.
If the car does not have a tachometer, you can determine the presence of problems by sounds. If there is something wrong with the engine, you will hear its roar either increasing or decreasing.
And during the inspection process, increasing and decreasing vibrations will be heard that penetrate into the interior of the vehicle, this will also mean the presence of problems.
Typically, unstable engine speed occurs at idle. However, even at intermediate speeds you can see how the tachometer needles do not behave as expected. Such cases most often occur when it comes to diesel engines.
Let's analyze both of these cases separately to understand what reasons contribute to this.
Speed jumps at idle
Floating idle speed occurs most often on injection engines. What is this connected with? First of all, because a special electronic engine control unit regulates the operation of the idle system.
Otherwise, it can be called the electronic “brains” of the car, which are needed in order to read data on idle speed. And when it starts to work incorrectly, the ECU reports this.
Then special sensors come into play and are responsible for the functioning of the system. They are the ones who should fix the problem.
Idle speed may become incorrect due to excess air entering the fuel system. Namely, into the engine cylinders. In this situation, the mass air flow sensor transmits information to the electronic control unit that excess has entered the combustion chamber.
When this happens, it is necessary to equalize the contents of air and fuel, which together create the fuel mixture. The unit sends a command to the injector valves to open and allow more fuel into the cylinders. At the moment when this happens, the engine speed increases sharply. And the ECU notes that a lot of fuel was supplied.
Therefore, it immediately limits its entry into the cylinders. Just at this time the speed drops noticeably.
The second reason for floating idle speed is incorrect operation of the idle speed controller.
The IAC is an electric motor that includes a cone needle. It is needed to stabilize engine speed when it is idling. The most common reason for its breakdown is the wear and tear of the spare parts that make it up. This happens when a car owner uses fuel for a long time, which is far from being of high quality.
Another reason for instability lies in the non-working condition of the oil crater ventilation valve. After all, when the engine is running, special gases accumulate in this crater. And if the motor is new, then the amount of such gases will be small, but a device that has been used for a long time cannot boast of this.
When the number of gases is excessive, they are removed by the ventilation system to the intake manifold and throttle valve. There they take part in creating a warm-air mixture in the combustion chambers of the engine.
And if the crater ventilation valve does not work correctly (this can happen due to deposits on the walls), then significantly less crater gases enter the intake manifold. Because of this, the engine speed begins to fluctuate.
There is another reason for the jump in revolutions. It consists in the fact that the mass air flow sensor fails. This part, like many others, becomes covered with a film of dirt and oil over time. And this leads to inevitable breakdown.
It is not often that the hot-wire anemometer in the sensor (responsible for measuring the volume of air that enters the combustion chamber) deteriorates. In such a situation, the ECU does not receive the necessary information about the mass air flow and wants it to be supplied to the cylinders.
This affects the speed jumps.
The last reason lies in the incorrect operation of the throttle valve, which should regulate the air pressure supplied to the engine cylinders. It may start to malfunction for several reasons:
- an unpleasant oil deposit forms on the inner surface of the damper “penny”, which prevents the device from opening and closing optimally;
- if the throttle valve actuator is faulty.
It is worth paying attention to the fact that the last reason is the most common. Therefore, it is necessary to consider it first.
Why do the revs fluctuate during intermediate travel?
Owners of cars with a diesel engine are faced with floating speed due to rust on the blades of the high-pressure fuel pump. And this happens because the fuel contains water. And for the same reason, diesel engine speeds fluctuate not only at intermediate speed, but also at idle.
The consequences of all this are varied: too high fuel consumption, release of exhaust gases into the environment, which contain a lot of CO, wear of parts of the fuel system, as well as the engine air supply system. To prevent all this from happening, you need to systematically check the functioning of the systems and elements listed above. And when problems have already occurred and the turnover is jumping, you need to immediately begin to correct the situation.
Elimination of floating engine speeds
- Air leaks into the engine cylinders. It is important to check the tightness of the air supply lines to the intake manifold. To do this, you need to remove each hose one by one and blow each one out. These hoses can also be treated with WD-40. In the place where the composition evaporates, you can see a crack. And it doesn’t need to be glued with insulating tape for it to last at least a little longer. It is preferable to replace the hose immediately.
- Replacing the idle air control. IAC analysis is done using a multimeter. If this device shows resistance in the range of 40 to 80 ohms, then the regulator will not work any further. You just need to throw it away and buy a new one instead.
- Cleaning the crater ventilation valve. In this case, you also need to disassemble the oil crater, because there is no other way to achieve ventilation. Next, you need to take out the valve and clean it thoroughly, first immersing it in kerosene or any other means intended for cleaning. After this, it needs to be dried and returned to its place.
- Replacing the mass air flow sensor. We are talking about a very fragile part, which in most cases is sent to the trash without the possibility of repair. Therefore, you should not attempt to repair it - it is better to immediately purchase a new one.
- Cleaning the throttle valve. This is done by washing with and without removal from the car. Everyone chooses their own cleaning option, however, after this process it is important to put the damper in place correctly.
- Correcting engine idle speed. This process can be carried out using just a screwdriver, adjusting the screws for the number and quality of revolutions.
- Replacing the carburetor solenoid valve. If this device breaks down, the engine can only operate on air suction. Therefore, in order to eliminate speed surges, you need to replace the carburetor valve with a new one.
- Cleaning the idle jet. Once upon a time, this process was incredibly difficult. But now you don’t even have to take out the jet to clean it. You just need to pour a special composition into it that will help clean it in the best possible way.
- Treatment of fuel injection pump blades from rust. Firstly, you will need a rust preventative here, and secondly, you need to remember that after cleaning, it is periodically necessary to pour about two hundred milliliters of motor oil into the tank for preventive maintenance.
Source: http://stotandem.by/blog/po-kakim-prichinam-plavaiut-oboroty-dvigatelia
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