Engine speed does not drop at idle: how to fix the problem. Why is the engine idle high and the engine speed does not drop?

While operating a car, drivers have to face various problems. One of the malfunctions, which is quite widespread, is the constant maintenance of high engine speeds. That is, even on idling Engine speed does not drop. This problem can occur in both injection and carburetor engines, but the reasons will be different. In this article, we will look at what malfunction this problem is a symptom of, and how you can get rid of it.

Table of contents:

How to diagnose that the idle speed does not drop

Even an inexperienced driver can easily notice that the car’s idle speed does not drop. This is easy to determine by ear, since, as is known, the lower the speed, the quieter the engine runs. In addition, if the car is equipped with a tachometer, it can be used to determine the number of revolutions per minute at a specific point in time.

Depending on what engine is installed in the car, the idle speed may vary. On average, an engine is considered to be operating normally when the idle speed is between 650 and 950 rpm. If the speed is higher (unless otherwise stated in technical passport to the car), then this can be called a deviation.

Please note: On most cars with fuel-injected engines, the “Check Engine” light on the dashboard will come on at high idle speeds.

What are the consequences of high idle speed?

The first thing a driver should remember is high flow rate fuel at increased speed. Accordingly, if high speeds remain at idle, this means that part of the fuel “flies into the pipe.” Moreover, this problem directly affects the life of the engine, which suffers as a result of such a malfunction. The node itself, which led to the occurrence of the malfunction in question, may also suffer. That is why, if this problem is identified, it should be eliminated as soon as possible.

Why does the idle speed of a carburetor engine not drop?

At the moment, carburetor engines are practically not used in modern cars. However, it is necessary to consider why high idle speed may be a problem in such engines, since most of the problems overlap with fuel-injected engines. If such a malfunction occurs, you should pay attention to the following elements:

Most of the problems that lead to high idle speeds are discussed above. carburetor engine. It also cannot be ruled out common problem for carburetors and injectors - jamming of the gas pedal.

Why does the idle speed of an injection engine not drop?

Now let's look at the malfunctions that lead to increased idle speed in an injection engine. Unlike carburetor engines, where all problems are of a mechanical nature, a malfunction in an injector can be associated, among other things, with improper operation of the electronics. The main reasons are as follows:

As you can see, there are quite a lot of problems due to which the idle speed does not decrease. If such a malfunction occurs, you should begin to find its cause as quickly as possible in order to prevent even more serious problems.

Often, car owners are faced with such a malfunction when, when releasing the gas, the engine speed does not drop, or more precisely, it does not drop to the normal idle level (idle). This applies to both the fuel injection system and the carburetor.

Usually the idle speed of gasoline passenger cars, depending on the engine model, are in the range of 650-1000 rpm. Any deviations from these indicators indicate incorrect operation of the vehicle's power system. There is no point in delaying the elimination of this malfunction, since increased engine speeds lead to increased fuel consumption in the car and accelerated engine wear, which negatively affects the driver’s financial condition.

Sometimes the reason may lie in the excessive enrichment of the fuel-air mixture supplied to the cylinders. This provokes an increase in speed to a certain level, after which the engine begins to “choke”, thereby reducing the speed to a normal value, after which it rises again. This malfunction causes a “floating speed” effect, but the problem may also lie in other malfunctions of the power system. In addition, do not forget that malfunctions in cases with injection and carburetor engines will be different.

Basic problems with an engine with a carburetor power supply system

The location of the needle valve, which is responsible for adjusting the gasoline level in the float chamber.
Loose closure throttle valve, which often happens when it is clogged or mechanically damaged. A dirty damper should be cleaned with a special product that can be purchased at an auto parts store. And in case of mechanical damage to this unit, most often it is required complete replacement carburetor
Incorrect adjustment of the XX system. This problem often appears after cleaning or replacing the carburetor. To eliminate it, you just need to adjust it, ensuring the optimal ratio of gasoline and air in the fuel-air mixture.
Consistently high idle speeds may indicate that the throttle valve located in the primary chamber is not tightly closed. This problem occurs due to wear of the throttle valve drive cable or deformation of the valve itself.
Damage intake manifold or wear of the gasket between the cylinder head or carburetor.

In the case of an injection power system, possible reasons promotion idle speed noticeably more. This is due to the fact that they can be associated both with the failure of mechanical components and with the malfunction of electronic sensors.

Main injector malfunctions

Coolant temperature sensor malfunction. Interruptions in the operation of this sensor lead to the fact that the engine constantly operates at high speeds, in warm-up mode. However, after warming up power unit to operating temperature the electronic control unit does not reset the speed to normal values, since the sensor signals that the engine has not yet warmed up. The same thing happens when the idle air regulator is not functioning properly.
Throttle adjustment cable stuck. This happens especially often on cars with high mileage.
Malfunction of the XX regulator or its electronic sensor, while the idle speed may increase or disappear altogether.
Throttle position sensor malfunction.
Jumping or excessive stretching of the return spring, which should return the damper to its original position.
Damage to the integrity of gaskets, rubber seals of injectors or the manifold itself. With these problems, excess air from the environment enters the combustion chamber.

The most common reason that the engine speed does not drop to idle when releasing the gas may be careless placement of a mat under the accelerator pedal after visiting a car wash.

Let's sum it up

First of all, a malfunction of the injection and carburetor power systems should begin to be diagnosed by inspecting the throttle valve.

In the case of injection engine, computer diagnostics will help to accurately determine the malfunction of a specific sensor. To do this, it is best to use the services of a service that specializes in servicing cars of a specific brand.

Increased engine speed at idle or while driving is a sign that the engine is not in 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 starting the engine, the speed rises to approximately 1500 RPM at idle. After the engine warms up, they drop to approximately 650-950 RPM, which is the norm. If after warming up the speed remains at the same level, then the engine is not working correctly.

The second option, when a defect occurs, is that the car does not fall when the gas is released while driving, that is, when braking with the engine and coasting. In this case, the speed seems to “freeze” above 1000 RPM up to full stop car, although in working order cars should fall below the specified mark.

Determining that a car is running at high speeds is quite simple. If dashboard The car is equipped with a tachometer, then the increased speed is displayed on it. In the case where there is no tachometer, the increased speed can be determined by the sound of the engine. The greater their number, the higher the tonality and louder the sound of the engine.

Main reasons

The reasons that the speed of the power unit does not decrease differ for 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 air fuel mixture into the combustion chambers. Most often, problems with high speeds are associated with an over-enrichment of the fuel-air mixture, but other causes of malfunction may also occur.

The effect of increased speed can be caused by the following problems.

Incorrect operation of the throttle valve responsible for the air supply. If the damper, after releasing gas or warming up the engine, cannot close tightly, and a gap forms in it, then an enriched fuel-air mixture enters the engine.
Open suction. Choke - a knob for adjusting the air damper, which is responsible for the flow of air into the carburetor. With its help, you can enrich the air-fuel mixture with air. If the suction is not working properly, the mixture becomes over-enriched with air.
Needle valve position. In this case, the incorrect dose of fuel will enter the combustion chamber. A malfunction of the needle valve can manifest itself in different ways, including the absence of a drop in speed.
Incorrect idle speed adjustment. This problem is often encountered by car owners who have changed or repaired the carburetor.
A fairly rare cause is a burnt-out cylinder head gasket. The problem is manifested not only by increased engine speeds, but also by the appearance of white smoke from the engine compartment.

On injection engines

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

The reason for the increased speed of injection engines may be one of the following problems.

Incorrect operation or failure of the coolant temperature control sensor. With such a malfunction, the engine constantly operates 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.
Sensor failure mass flow fuel sensor (MAF), which is also called the idle air sensor. A malfunction of the mass air flow sensor can manifest itself in different ways - a loss of speed or an 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 may 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.
Sticking throttle cable.
Damage to the injector gaskets.

What to do

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

Incomplete closing of the throttle valve most often occurs due to the formation of carbon deposits from combustion products. In this case, you just need to clean it with carb cleaner. If the throttle valve does not close completely due to a chip or crack, it will need to be replaced.
A suction malfunction can be eliminated by lubricating the cable and the air damper drive.
The problem of the needle valve is solved by replacing the part.
An incorrectly adjusted idle speed can be corrected by adjusting it correctly.
The blown cylinder head gasket is replaced with a new one.

Solving problems with electronic sensors of injection engines is almost always solved by replacing them. Their malfunction is manifested by the appearance of the inscription Check Engine, after diagnosing 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 faults.

How to avoid the problem

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

Another reason that the speed is maintained while driving may be the mat sticking behind the gas pedal. In this case, the accelerator pedal does not go down completely, which leads to excessive enrichment of the fuel-air mixture. To prevent the problem, you just need to adjust the rug.

Many owners of injection cars could observe the effects when the idle speed suddenly drops. This phenomenon occurs especially often when the engine is warmed up to operating temperatures. Sometimes the revs drop so low that the engine stalls. Let's figure out what can cause low idle speeds on a warm engine, and also find out why they drop. This information will be useful to everyone.

The origins of unstable engine operation at XX

How will the picture develop if the control unit does not receive data on the quantity and volume of air consumed? So, for example, the reaction of the throttle sensor will be as follows - the speed will initially increase, but then the fuel mixture will begin to become leaner, as a result of which low speeds will be established on a hot engine. There is only one reason for this - the amount of air consumed by the engine has decreased.

However, the opposite happens - the fuel mixture becomes richer, and the engine begins to gain speed again. Such cycles can alternate endlessly; these are floating revolutions. The problem of low idle speed on a warm engine in winter is especially pressing.

On some cars, events may develop differently - the speed increases, for example, to 2000 rpm, and remains there. The reason is that the injector injects increased amounts of fuel. The amount of air does not increase, otherwise the engine would be able to increase the speed to 3 thousand, however, then it would still start to stall.

Fuel quality

When the idle speed drops on a warm engine, you should not discount fuel. It is possible that the problem is not related to the electronics, sensors or actuators. Maybe the whole point is that the driver fills with lower octane gasoline, and the ECU is designed for high-octane brands. Hence the lean mixture, so the control unit has no choice but to work like this.

Possible reasons

So, what causes this problem? Some of the most vulnerable links in injection engines are sensors. One of the elements that directly affects engine performance and quality is the idle speed sensor. You can often find it near the throttle valve. This is a stepper motor with a tapered locking needle. When the throttle is closed, air bypasses the damper through the idle channel, which is blocked by the needle.

Another culprit for very low idle speed is Air - the second important component for preparing the fuel mixture after gasoline. Therefore, if the mixture is lean enough, then high speeds will not come from anywhere.

When malfunctions occur in the system, the ECU cannot correctly select and calculate the proportions of the fuel mixture in idle mode. As a result, the engine operation will be unstable, the speed will begin to fall and rise.

A less common problem with low idle speeds on a warm engine can be improper operation of the EGR system, or more precisely its valve. The element is installed in the intake manifold and its function is to remove exhaust gases. This is nothing more than Periodically the sensor needs to be cleaned.

It would also be a good idea to make sure that there is no air leak in the system and check the condition of the throttle valve. Often the problem of low speeds can be associated with a dirty valve or its mechanical damage or deformation. It often happens that for one reason or another the valve jams - hence another reason for low speeds.

Why do sensors die?

Experts identify two reasons for low idle speed. One of them is related to low fuel quality. Often underestimated octane number not only greatly contaminates the working surface of the sensor, but can also cause various malfunctions in the operation of electronic units.

In addition, sensors often fail due to banal defects or exceeding their service life. Inexpensive sensors may well turn out to be of low quality or defective. This is why low idle speeds appear on cars.

How to prevent air leaks?

In order to exclude or confirm the leakage of excess unaccounted air into the system, check the tightness of the air supply system.

To do this, you can remove the air pipe and blow into it from a compressor or pump. The hose can be placed in water. This will reveal cracks and other defects.

How to check the idle speed sensor?

To check the functionality of the sensor, it is recommended to use a multimeter. The verification procedure is very simple. Replace the resistance between the contacts in the sensor block. It is important that the ignition is turned on. The resistance between different pairs of contacts should be between 39.5 and 81 ohms. If during measurements the multimeter gives different readings, then the sensor should be replaced.

Checking the mass air flow sensor

So, first, to check, turn on the ignition. You need to check the voltage with a multimeter. Measure it between the contacts with the green and yellow wires. On various cars the voltage can vary from 0.9 to 1.2 V. You can determine if the mass air flow sensor has failed and by appearance spark plugs - black carbon deposits indicate that it is better to replace them.

How to clean the idle air control (IAC)?

When there is a problem with low idle speed on a warm engine, in some cases it can be eliminated by flushing the IAC. To do this, de-energize the car. The regulator is located on the throttle assembly, below the TPS (throttle position sensor). You should prepare a clean rag, a screwdriver, liquid in an aerosol can - this can be any product for cleaning carburetors or injectors.

Cleaning begins with dismantling - to remove it, just unscrew the mounting screws. Sometimes there are also bolts. Once the sensor has been removed from its mounting location, the cleaning process can begin. The work is carried out using rags treated with liquid from a spray can.

It is also necessary to spray the needle from the can. The latter on various car models can be either metal or plastic. The cleaner will not damage the plastic. But the liquid should not get under the spring. If this does happen, it is recommended to blow out the sensor with compressed air as quickly as possible. If this is not done, the liquid will wash out the internal lubricant, which will cause complete failure of the IAC.

Conclusion

As you can see, only a few sensors can provoke low engine speeds at idle. But even one small element can significantly ruin the life of the car owner, especially if the speed does not always drop. But this is not a problem, because this issue can be solved easily, without large investments.

Typically, the idle speed of gasoline passenger cars, depending on the engine model, is in the range of 650-1000 rpm. Any deviations from these indicators indicate incorrect operation of the vehicle’s power system. There is no point in delaying the elimination of this malfunction, since increased engine speeds lead to increased fuel consumption in the car and accelerated engine wear, which negatively affects the driver’s financial condition.

Basic problems with an engine with a carburetor power supply system

The location of the needle valve, which is responsible for adjusting the gasoline level in the float chamber.
The throttle valve does not close tightly, which often happens when it is clogged or mechanically damaged. A dirty damper should be cleaned with a special product that can be purchased at an auto parts store. And in case of mechanical damage to this unit, most often, a complete replacement of the carburetor is required.
Incorrect adjustment of the XX system. This problem often appears after cleaning or replacing the carburetor. To eliminate it, you just need to adjust it, ensuring the optimal ratio of gasoline and air in the fuel-air mixture.
Consistently high idle speeds may indicate that the throttle valve located in the primary chamber is not tightly closed. This problem occurs due to wear of the throttle valve drive cable or deformation of the valve itself.
Damage to the intake manifold or wear of the gasket between the cylinder head or carburetor.

In the case of an injection power system, there are much more possible reasons for the increase in idle speed. This is due to the fact that they can be associated both with the failure of mechanical components and with the malfunction of electronic sensors.

Main injector malfunctions

Coolant temperature sensor malfunction. Interruptions in the operation of this sensor lead to the fact that the engine constantly operates at high speeds, in warm-up mode. At the same time, after the power unit warms up to operating temperature, the electronic control unit does not reset the speed to normal values, since the sensor signals that the engine has not yet warmed up. The same thing happens when the idle air regulator is not functioning properly.
Throttle adjustment cable stuck. This happens especially often on cars with high mileage.
Malfunction of the idle regulator or its electronic sensor, in which case the idle speed may increase or disappear altogether.
Throttle position sensor malfunction.
Jumping or excessive stretching of the return spring, which should return the damper to its original position.
Damage to the integrity of gaskets, rubber seals of injectors or the manifold itself. With these problems, excess air from the environment enters the combustion chamber.

The most common reason that the engine speed does not drop to idle when releasing the gas may be careless placement of a mat under the accelerator pedal after visiting a car wash.

Let's sum it up

First of all, a malfunction of the injection and carburetor power systems should begin to be diagnosed by inspecting the throttle valve.

In the case of an injection engine, computer diagnostics will help to accurately determine the malfunction of a specific sensor. To do this, it is best to use the services of a service that specializes in servicing cars of a specific brand.