Engine speed does not drop at idle speed. High idle speed are possible causes. Major engine problems with a carburetor power system

High engine idle speed, apart from completely unnecessary excessive fuel consumption, also interfere with driving - for example, when driving through a particularly broken section of the road, when you want to carefully “sneak” among potholes in first gear, and the car boldly takes impacts on the suspension. In addition, during long periods of inactivity in traffic jams, the motor will operate at an increased temperature all the time.
Let's consider several reasons why the increased idle speed does not fall on a warm engine. The reasons can be malfunctions in both the mechanical and electronic components of the engine power supply system, therefore, we will describe the possible options for breakdowns separately. But since in a car these components interact in a complex, then perhaps you can independently find the answer to the question of why your engine has high idle speeds, taking the material of this article as "information for thought."

Checking the intake manifold for leaks

Excessive air leaks can cause high idle speeds. Moreover, depending on the place of penetration of excess air into the intake manifold, the idle speed will either be simply increased, or will start to "float" -.

If the idle speed "floats", then most likely it is.

If there is simply a violation of the tightness of the intake manifold gaskets, damage to the vacuum hoses or O-rings, then the revolutions will "float". This is due to the fact that the amount of gasoline supplied to the cylinders will be constant, and the quality of the mixture becomes "richer", then "poorer". When a certain critical value (air content in the fuel mixture) is reached, the engine will start to slow down - up to a stop. But with a decrease in the number of revolutions, the amount of air entering the manifold will decrease, that is, the mixture will be enriched and the engine will "come to life" - the idle speed will increase. This will continue until the tightness of the intake manifold is eliminated.
On turbocharged engines, air can also be sucked in through damage to the intercooler or the connections of the air pipes. In case of significant suction (for example, if the pipe has come off the intercooler), the engine starts to work with a hissing (or hissing) sound. But sometimes it is possible to identify the place of violation of the intake tract only by shutting off the air supply to the intake manifold in different places in turn - from the air filter to the manifold itself.

Excess fuel supply

Cleaning the throttle valve

A completely different situation will turn out if not just excess air flows, but a fuel-air mixture - for example, through a gap formed as a result of a loose closing of the throttle valve. In this case, high idle engine speeds will be stable.
In the fuel systems of some engines, a semi-automatic regulation of the fuel supply is provided in the engine warm-up mode - due to it, high idle speeds are maintained until the engine warms up to a predetermined temperature. Fuel is supplied through a channel that "bypasses" the throttle valve.
Such a channel can be closed / opened in various ways - the valve in it has either an electric drive (solenoid), or it can be arranged like a refrigerator thermostat - when the engine warms up, the channel is locked.

At high idle, check the entire throttle body assembly with sensors and XX regulator.

In any case, such a valve may break, and then excess fuel will always flow into the intake manifold, which will cause high idle speed after the engine has warmed up.
In all such cases, first of all, you need to remove the throttle body and rinse it with a special solution - a lot of such "chemistry" is sold in stores. After flushing, you need to carefully inspect the assembly - especially for jamming or, on the contrary, excessive looseness of the throttle valve.
The throttle valves of some injection engines have, in addition, a screw for adjusting the engine idle speed or limiting the closing of the throttle - you should pay attention to them, - whether the unit can be adjusted.
Often, the engine speed does not drop at idle speed due to jamming of the throttle cable or foreign objects falling under the pedal - the corner of the mat, for example.
Of course, almost all of the above can also apply to carburetor engines. In addition, a typical malfunction (or, more precisely, a deviation from the norm) for them is incomplete opening of the air damper - mainly due to improper installation of the "suction" cable. In the absence of breakdowns, the normal idle speed of the carburetor engine is set by adjusting using two screws - the "quantity" and "quality" of the mixture.

Electronics failures

Checking the engine idle speed control

After replacing the idle speed regulator, it must be "registered" ie. enter its parameters into the ECU memory.

The idle speed controller (IAC) is a stepping motor (solenoid) powered by pulse signals supplied. It works in a similar way to the screw for adjusting the amount of mixture in the carburetor - when the valve is extended, it closes the fuel channel, during the return stroke it opens it.
It often happens that the regulator core simply jams and it stops responding to ECU signals. Moreover, you can damage the idle speed regulator even in the store when buying - by trying to turn or press the valve needle with your hands.
If, after replacing the idle speed sensor (regulator), high speed occurs, then most likely the matter is either in the ECU or in the mass air flow sensor - all the elements of the power system work in concert, and diagnostics need to be carried out. It is quite possible that you will have to "register" a new regulator - that is, enter its parameters into the ECU memory.

temperature sensor

This sensor can also affect the fuel system of the engine. By giving an incorrect signal (corresponding to a low temperature) to the ECU, it will cause the controller to give a signal to other elements of the fuel system (injectors, including) about the enrichment of the mixture. An incorrect sensor signal will lead to the idle speed being more than 1000 min-1.

Mass air flow sensor

Mass air flow sensor directly affects the quality and quantity of the mixture supplied to the cylinders - after all, the ECU "knows" about its composition thanks to this (and some other) sensors.
In conclusion, if the idle speed of the engine of your car unreasonably increased, first look for the cause in possible jamming of the fuel system mechanisms - after all, they are primarily exposed to various contaminants, and voltage surges or short circuits are much more dangerous for electronic components.

Drivers often wonder why the engine idle speed does not drop. This situation is quite common, and neither carburetor engines nor more modern injectors are immune from this. True, the reasons for the malfunction will be different for them. But, in practice, everything can be diagnosed independently, and also on almost all car models, the problem can be eliminated by hand without much difficulty. The most important thing here is to correctly diagnose, this will significantly speed up the repair process, and save you from additional problems and difficulties.

What it is?

Why does the engine idle speed not drop? First, let's decide how to understand that there is a problem, and also see what it can lead to. Even an inexperienced motorist can determine the increase in idle speed. It can be easily felt by ear. With an increase in revolutions, an increase in the noise of the engine running is observed when the gas pedal is released. Also, on cars equipped with a tachometer, you can track the increase in revolutions on the device. On almost all models of passenger cars, idle speed fluctuates within 650-950 rpm(check the indicator in the technical passport of your car), everything above is considered a deviation from the norm. Also, on many injectors, this problem is caused by the inclusion of a "check" on the panel.

In any case, you should try to fix the problem as soon as possible. Higher revs are the reason for an increase in fuel consumption. This increases the cost of refueling. Also, an increase in revs significantly accelerates engine wear. So it is not advisable to delay the solution of this problem. This will save you a lot of money. When identifying and eliminating the cause of high rpm, it should be remembered that on carburetors and injectors, the problem can be caused by various malfunctions.

Carburetors

First, let's deal with the problem on carburetor engines. This type of power supply is considered obsolete, but there are still many vehicles on the road that are stocked this way. Also, many motorists, for their ideological reasons, use such motors, and are not going to give them up. It is quite difficult to diagnose the source of the problem here, and this is given the small list of items causing an increase in revs. Let's take a look at what you should pay attention to:

Needle valve engagement... In this case, the fuel enters the chamber in a non-metered manner. Moreover, depending on the location in which the valve is jammed, idle turns can both disappear and vice versa increase;
Violation of regulation idle system. This usually happens after cleaning or repairing the carburetor. To avoid problems, the ratio of fuel and air should be set correctly. If you have not previously produced, then it is better to read how this is done exactly on your version;
Closing problem. There may be several reasons for such a malfunction. Most often, the damper does not close due to the presence of carbon deposits on it. In this case, you will need to clean this node. This usually helps. In some cases, the throttle valve may be damaged. Then you will need to change this part, but not all carburetors have this option;
Sometimes, the problem can appear when, this happens quite rarely. But, it's still better to check. To do this, with the engine running, open the radiator cap; with a burned-out gasket, white smoke will come out of the neck. In this case, you will need to change the gasket;
Open suction... Check how the damper in the primary chamber works. If you have identified a problem, then it makes sense to see how the suction works. Most often, to fix the problem, it turns out to be enough just to lubricate the cable and the damper drive.

In addition, jamming of the gas pedal may occur. This situation can happen not only on carburetors, but also on injectors. Be sure to check if the pedal moves freely.

Injector

On engines equipped with injectors, there are more possible reasons for increased revs. In particular, the problem can be caused by both mechanical failures and the failure of electronic sensors. But, unlike simpler carburetors, it is simplified by the presence of an on-board computer that is able to read errors. So, let's consider the reasons for the increase in speed on the injectors:

Refusal . If this sensor breaks down, the power unit begins to work non-stop in the warm-up mode, that is, the revolutions are not reset. The control unit considers that the optimum operating temperature has not yet been reached and tries to heat the unit. Such a malfunction is fraught with engine overheating and costly repairs. The easiest way to identify this problem is through computer diagnostics;
Disruption of work. Sometimes, the cause is the mass air flow sensor. Again, they make diagnostics, after which they check the suspicious sensors with a multimeter. An additional check is required to ensure that there is no open circuit in the wiring. If necessary, faulty sensors are changed;
Throttle cable sticking may occur. Check if it works. If a malfunction is identified, it is recommended to try to lubricate the cable and develop it. If it does not help, then you will have to replace the part completely;
The damper return spring has jumped off or is too stretched. This problem is also common in older vehicles. Replace the spring. If it is stretched, then you will need to buy an injection repair kit;
... In this case, it sends a signal to the engine control unit about the open throttle, in turn, the "brains" of the car provide more revolutions than it actually needs. The cause of the breakdown may be a simple jamming of the part, or a burnout of the resistance. In the latter case, only the option with replacing the sensor is possible;
The last reason to check is integrity injector gaskets... The check will require a fairly serious intervention in the injector, therefore, this reason is checked last, although this phenomenon is not the rarest. If the gaskets are damaged, excess air enters the combustion chambers, which causes an increase in engine speed.

In addition to all of the above, always monitor the location of the mat in the car, sometimes it gets under the pedal and does not allow it to work optimally.

Conclusion... Every motorist has encountered problems with the operation of the power system at least once. Therefore, such a question as to why the engine speed does not drop at idle is not surprising. Unfortunately, it is almost impossible to answer it unequivocally. There are many reasons for this behavior of the car. To identify and eliminate the breakdown, you will have to carry out detailed diagnostics.

Increased engine speed when idling or while driving is a sign that the engine is out of order. This behavior of the power unit leads to increased fuel consumption and increased wear of engine parts. Therefore, this defect must be eliminated as soon as possible.

Description of the problem

When the engine is started, the speed rises to about 1500 rpm at idle speed. After the engine warms up, they drop to about 650-950 RPM, which is the norm. If, after warming up, the revolutions remain at the same level, then the motor does not work correctly.

The second option, when a defect occurs, is the absence of the car falling when the gas is released while driving, that is, when braking with the engine and coasting. In this case, the revolutions seem to "freeze" at a level above 1000 rpm until the car comes to a complete stop, although in serviceable cars it should fall below the indicated mark.

It is quite easy to determine that the machine is operating at high revs. If the dashboard of the car is equipped with a tachometer, then the increased speed is displayed on it. In the event that there is no tachometer, then the increased speed can be determined by the sound of the engine. The more there are, the higher the tonality and the louder the sound of the engine.

Main reasons

The reasons why the speed of the power unit does not decrease differ between cars with injection and carburetor engines.

On carburetor engines

In cars equipped with carburetors, it is this unit that is responsible for preparing and supplying the air-fuel mixture to the combustion chambers. Most often, problems with increased speeds are associated with re-enrichment of the fuel-air mixture, however, other causes of malfunction may also occur.

The overspeed effect can be caused by the following malfunctions.

Incorrect operation of the throttle valve, which is responsible for the air supply. If the damper cannot close tightly after discharging gas or warming up the engine, and a gap forms in it, then an enriched fuel-air mixture enters the engine.
Open suction. Suction is a knob for adjusting the air damper, which is responsible for the flow of air into the carburetor. It can be used to enrich the fuel-air mixture with air. If the suction is not working properly, the mixture is re-enriched with air.
Needle valve bedding. In this case, the wrong dose of fuel will enter the fuel combustion chamber. A malfunction of a needle valve can manifest itself in different ways, including the absence of a drop in speed.
Incorrect idle adjustment. This problem is often faced by car owners who have changed or repaired the carburetor.
A fairly rare reason is a burnout of the cylinder head gasket. The problem is manifested not only by increased engine speed, but also by the appearance of white smoke from the engine compartment.

On injection motors

For cars equipped with injection engines, the range of reasons for increased revs is wider. This is due to the fact that in such machines there are much more electronic devices and sensors responsible for transmitting information to the electronic control unit that regulates the engine speed. Therefore, violations of the engine operating mode can be associated with mechanical damage, and with a malfunction of electronic systems.

One of the following problems can be the cause of the increased speed of injection engines.

Incorrect operation or failure of the coolant temperature control sensor. In the event of such a malfunction, the engine constantly runs in warm-up mode, since the ECU (electronic control unit) does not receive information from the sensor that the engine is already warmed up. As mentioned above, in this mode, the engine speed is increased.
Breakage of the mass fuel flow sensor (MAF), which is also called the idle sensor. A malfunction of the mass air flow sensor can manifest itself in different ways - by the loss or increase in speed. In the latter case, the engine also goes into constant warm-up mode.
Throttle position sensor malfunction. In this case, a sensor malfunction can be perceived by the ECU as information about an open throttle valve. Then the control unit gives a command to increase the speed.

Also, the reasons for the increased speed of injection engines can be associated with mechanical damage.

Broken throttle return spring.
Stuck throttle cable.
Damaged injector gaskets.

What to do

To solve the problem, you need to diagnose it. On cars equipped with carburetor engines, faults are consistently checked and corrected.

Incomplete closure of the throttle valve most often occurs due to the formation of carbon deposits from combustion products. In this case, it just needs to be cleaned with a carbcliner. If the throttle valve does not close completely due to a chip or crack, then it will have to be replaced.
The suction malfunction can be eliminated by lubricating the cable and the choke actuator.
The needle valve problem is solved by replacing the part.
An incorrectly set idle speed can be corrected by adjusting it correctly.
The burned-out cylinder head gasket is replaced with a new one.

The solution to problems with electronic sensors of injection engines is almost always solved by replacing them. Their malfunction is manifested by the appearance of the Check Engine inscription, after diagnostics with a scanner, you can get an error code indicating a specific problem. You can also use a multimeter in ohmmeter mode to diagnose sensor malfunctions.

How to avoid the problem

If all parts and assemblies of the car are in order, then the problem in cars equipped with fuel injection may lie in the ECU firmware. It is the control unit that regulates the engine speed and the composition of the air-fuel mixture entering the cylinders. To avoid in the future the problem of maintaining high speeds after the gas is released or the engine warms up, you can reflash the electronic control unit.

Another reason that the revs are maintained while driving may be a mat falling behind the gas pedal. In this case, the accelerator pedal does not fully descend, which leads to excessive enrichment of the fuel-air mixture. To prevent the problem, you just need to fix the rug.

It is essential that all powertrain systems are working properly. In this case, the engine should operate normally both under load and in idle mode.

In practice, drivers often encounter a problem when, after the throttle is released, the engine speed does not fall or falls with a long delay. It is quite obvious that excessive idle speed indicates a problem and is the cause of increased fuel consumption.

In this article, we will talk about why the engine speed does not fall, and also consider the main reasons why such problems arise in cars.

Read in this article

When throttle is released, the RPM is increased or "freezes": common malfunctions

Let's start with the fact that on many cars with an injector, it rises during warming up. This is necessary in order for the power unit to operate stably after a cold start.

However, after the temperature rises, the control unit lowers the speed of XX, bringing them to normal. On many cars with a carburetor, the driver independently increases the speed during warming up, using the so-called "suction".

Moreover, after the engine is warmed up, the idle speed is, on average, 650-950 rpm. If you press the gas and release the accelerator, the revs should increase, and then drop again to the specified values.

Also, a situation often arises when the revolutions are slowly dropped or are constantly kept at the level of 1.5 thousand rpm, 2 thousand revolutions, etc. Naturally, in such cases, the consumption increases and the internal combustion engine wears out more, which indicates the need for diagnostics.

So let's start with the common carburetor problems. Often times, the engine speed will not drop due to throttle problems. For example, when the driver presses on the gas, the throttle must be opened wider to allow more air to enter the cylinders for fuel combustion. After the gas pedal is released, the damper closes, the speed decreases.

If the damper does not close completely, the re-enriched mixture enters the cylinders, the revolutions are increased. This may be due to heavy contamination of the throttle assembly or damage to the damper itself (deformation). First you need to clean the damper; carburetor cleaning fluid is suitable as a cleaner.

We also note that the damper does not close tightly even when the drive cable is worn out. In this case, the cable must be replaced. On carburetor machines, engine speed does not drop often even if the gasket between the carburetor is out of order. Also, the intake manifold, which is damaged, may be the culprit.

The main challenge is to find the right ratio of fuel and air. Often, a high level of fuel in the carburetor's float chamber will also lead to increased revs. The test should start with the needle valve.

Now let's move on to the injector. Pay attention to many injection cars. As for the malfunctions, the injection system itself is more complicated, that is, there are more reasons for high rpm compared to the carburetor.

Typically, speed problems can be caused by malfunctions of both mechanical and electronic components. In the list of major malfunctions, experts highlight malfunctions of the coolant temperature sensor, which is installed in.

In simple words, if the specified sensor gives a wrong signal, the ECU considers that the engine is cold and activates the warm-up mode. In this case, the control unit raises the speed so that the power unit works stably and reaches operating temperature faster.

Also, speed problems can begin due to malfunctions and malfunctions (idle speed controller). It also happens that the throttle cable sticks and wedges. Also, the spring that closes the throttle can be stretched or damaged.

Special attention should be paid to gaskets, since air leakage can lead to the violation of mixture formation. This means that it is necessary to separately inspect the manifold gaskets, injector seals, etc.

Floating revolutions: reasons

Note that in some cases the turnovers do not just slowly fall or stay at the same level, but “float”. In this case, the engine may become unstable. first they fall, then they rise sharply and everything repeats. A frequent cause of this phenomenon is the supply of excess air, which leads to "jumps" in revolutions at XX.

Such problems arise in the event of a failure of the air supply sensor (), which allows the ECU to calculate how much air has entered and how much fuel to supply to prepare the required mixture.

If malfunctions occur, the control unit cannot prepare the "correct" mixture for the XX mode, which causes jumps in revolutions after releasing the gas pedal or when the engine is idling.

Let's summarize

As you can see, in many cases, in-depth diagnostics may be necessary in order to determine exactly why the engine speed is not dumping. For carburetor engines, cleaning and adjusting the carburetor itself is often necessary, while an injector will.

If the problem does not lie on the surface (the damper cable is acidic, after washing or dry cleaning, the carpet in the cabin is incorrectly placed, which presses the gas pedal, etc.), then it is better to take the car to the service.

The most difficult situation is when it involves a large number of sensors and actuators. In this case, even the use of diagnostic equipment does not always allow you to quickly and accurately determine the problem.

If the diagnosis is difficult, it is optimal to deliver the car to a service that specializes in the repair of a particular car brand. As a rule, these are official dealer service stations, less often you can find third-party organizations.

Finally, we note that the timely detection of the problem allows you to save other components and assemblies. In other words, high rpms, rpm float and jumps indicate that there is a problem with the air / fuel supply or mixture formation. Ignoring these problems will negatively affect the engine and its service life.