Which is necessary to maintain the fuel combustion process in the cylinders at a minimum level, that is, so that the engine continues to operate and does not stall. On different engines, the idle speed may differ and also depend on the temperature of the internal combustion engine. If the indicated idle speed increases, the engine begins to consume more fuel, and the exhaust in this mode becomes more toxic. A decrease in idle speed leads to unstable operation of the power unit, as well as to the fact that the engine begins to stall after releasing the gas pedal. In this article we will talk about what could be the reason for high engine idle speeds, why high idle speeds on a warm engine are found in many cars, and also consider the main ways to diagnose this malfunction.
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High engine speed at idle: injector
Engine speed and operation at idle actually means that air is supplied to the engine bypassing the throttle valve. In other words, at idle the specified damper is closed. Note that the normal idle speed for different units is about 650-950 rpm. In parallel with this, a common malfunction is that when the engine is warm, the idle speed remains at around 1500 rpm and above. This indicator is a sign of a malfunction that should be eliminated.
It should also be noted that the idle speed “floats”, that is, for example, it increases to 1800 rpm, after which it decreases to 750 and increases again. Very often, increased idle speed and floating speed are the result of the same breakdowns. Let's take a look at a gasoline-injected unit as an example. In such an internal combustion engine, engine speed depends on the amount of intake air. It turns out that the more the throttle valve opens, the more air enters the intake manifold. Then it determines the amount of incoming air, at the same time takes into account the throttle opening angle (throttle position) and a number of other parameters, after which it supplies the appropriate amount of gasoline.
If the ECU does not have accurate information about the amount of air due to a malfunction, then the following will happen: the controller will first raise the speed, enriching the mixture (more fuel is supplied). Then, with so much fuel and an additional volume of air that the ECU does not know about, the mixture will become leaner, and the engine will begin to operate unstably or may almost stall. In other words, the revs will start to drop when the mixture is too lean. Reducing the speed means that the amount of air sucked in by the unit also decreases. At a certain point, the mixture (fuel to air ratio) will again be optimal, causing the speed to rise again and then begin to fall or “float”. The reason for this operation of the internal combustion engine may be that it has failed or is operating intermittently. You should also take into account possible air leaks at the inlet.
Another case is when the engine keeps the idle speed at about 1500-1900 rpm, while running smoothly, the speed does not fluctuate. In this case, we can assume that the injector supplies enough fuel in idle mode that it is enough to operate at such high speeds. In other words, there is excessive fuel consumption. These features may be typical for some engines and absent for others, since there is a dependence on the design of a specific injection system (units with an air flow meter, engines with a pressure sensor in the intake manifold). It is obvious that air leaks are a common cause of increased engine speed or floating speed at idle.
Now let's figure out where excess air can enter the intake. You should look for the problem in four main directions:
- throttle valve;
- channel XX;
- device for maintaining “warm-up” speed;
- servomotor for forced increase in speed XX;
As for the first case, the opening of the throttle valve is controlled by the gas pedal. At idle, the engine should run without pressing the accelerator. It is worth considering that on many cars the gas pedal is mechanical, that is, it is connected to the throttle opening mechanism with a regular cable. If this cable is soured, kinked or overtightened, and problems arise with the mechanism itself, then a banal effect of pressing the gas pedal may occur. In this case, the engine will maintain increased speed, since the ECU believes that the driver is pressing the accelerator and the throttle is slightly open.
In the second case, excess air can pass through the idle passage. Such a channel is available on the vast majority of injection internal combustion engines. This air channel bypasses the throttle valve and is called the idle channel. The implementation of the circuit has a special adjusting screw. Using this screw, you can change the cross-section of the channel, thereby increasing or decreasing the amount of air entering the engine and adjusting the idle speed.
Another place where air leaks are possible is a device that maintains high idle speeds while the internal combustion engine is warming up. To put it simply, there is a separate air channel, which contains a solution for closing it after the engine warms up (rod or damper). The shut-off device itself contains a sensitive thermoelement. On many units, this element interacts with antifreeze in a similar manner. On a hot engine, the device operates in such a way that the rod extends completely or the damper rotates at such an angle as to completely block the channel for supplying additional air.
As a result, the ECU calculates the amount of air, reduces the amount of fuel supplied and the speed decreases. If the engine is cold, this channel is initially open. In this case, the ECU receives readings from the temperature sensor and enriches the fuel mixture. Problems with speed can arise either as a result of the failure of this device or after a malfunction of the temperature sensor.
The list is completed by a special servo device - the idle air regulator, which is installed in a separate air channel. This solution can forcefully increase idle speed. In various circuits, this could be an electric motor, a solenoid, a version of a solenoid valve, etc. The main task of such a regulator is to ensure a smooth transition of the engine to idle mode after releasing the gas pedal. In other words, the engine does not suddenly reduce speed after closing the throttle, but gradually. Another function of the device is to increase idle speed when the engine starts, and then smoothly reduce it to the required speed. The regulator also increases the speed after increasing the load on the internal combustion engine in idle mode (turning on the air conditioning system, heated seats or mirrors, high or low beam headlights, side lights, etc.). Failure of this device will naturally lead to an increase or floating of idle speed.
Increased idle speed on engines with a carburetor
At the very beginning, we note that an increase in idle speed on carburetor engines is often associated with the metering device itself. If high engine speeds are noted at idle in the case of a carburetor engine, then there may be several reasons.
- The first reason is a broken idle speed control. This adjustment is carried out using an adjusting screw, which allows you to enrich or lean the mixture. To solve the problem, you must correctly adjust the idle speed on the carburetor.
- You should also pay attention to the fact that the air damper may not open completely on carburetor cars.
- Another place to pay attention is the first chamber choke in the carburetor. The specified damper may not close completely due to defects in the damper itself or an incorrectly adjusted actuator.
- Finally, we add that a noticeable increase in the fuel level may be observed in the carburetor float chamber, which also leads to an increase in idle speed.
What's the result?
It should be noted that the idle problem on an engine with an injector is diagnosed by checking the main systems that are responsible for the flow of air into the internal combustion engine, as well as changing the mixture composition taking into account the amount of incoming air. It turns out that you should also take into account the fact that the failure of individual ECM sensors can lead to an increase or floating idle speed.
In the general list of the main reasons why idle speed can increase on the injector, there are: idle speed regulator, TPS, power unit temperature sensor, problems with the throttle valve opening control mechanism, intake air leaks. Let us add that before in-depth diagnostics, you should first carry out the procedure for cleaning the throttle valve, since a dirty throttle is a common cause of increased speed or unstable operation of the engine at idle.
Read also
Why do you need to clean the throttle valve periodically? How to clean the throttle valve, training and adaptation of the throttle valve after cleaning, useful tips.
description
The procedure is to teach the ECM to supply air at idle speed while maintaining engine speed within normal limits. It must be performed in the following cases:
When replacing the electric throttle actuator or ECM;
When the speed is idle. or the ignition timing is different from the norm.
1. preparation
Before performing the air supply training procedure at idle speed. Make sure the following conditions are met. The training procedure is canceled if one of them is not followed even for a moment.
Battery voltage: more than 12.9 V (at idle speed);
Engine coolant temperature: 70-100 "C;
PNP switch in “ON” position;
Electrical load switch: in position “OFF” (air conditioning, headlights, rear window defroster).
On vehicles equipped with daytime running lights, set the light switch to position 1 to turn on only small lights.
Steering wheel: in neutral position (corresponding to straight-line movement);
Vehicle speed: vehicle is stationary;
Gearbox: warmed up;
On models with CVT and manual transmission:
Travel by car for 10 minutes.
2. execution procedure
If there is a malfunction in the accelerator pedal position sensor circuit, switching to diagnostic mode is not possible.
1. Perform the accelerator pedal release position learning procedure. See above.
2. Perform the closed throttle learning procedure. See above.
3. Start the engine and warm it up to normal operating temperature.
4. Turn the ignition key to the “OFF” position and wait at least 10 seconds.
5. Make sure the accelerator pedal is fully released, turn the ignition key to the “ON” position and wait 3 seconds.
6. Repeat the following procedure quickly five times within 5 seconds:
Press the accelerator pedal fully.
Release the accelerator pedal completely.
7. Wait 7 seconds, fully depress the accelerator pedal and hold it for approx. 20 seconds until the “MI” fault indicator stops flashing and lights up steadily.
8. Fully release the accelerator pedal within 3 seconds after the malfunction indicator “M|” comes on.
9. Start the engine and let it run at idle speed.
10. Wait 20 seconds.
Go to step 3.
3. check the idle speed. and ignition timing
Boost the engine two or three times and make sure that the idle speed is and the ignition timing is normal.
Are the test results normal?
Yes ->End check.
No -> Go to step 4.
4. Identify the faulty component
Check the following:
Check if the throttle valve is completely closed.
Check the operation of the PCV valve.
Check for air leaks behind the throttle valve.
Are the test results normal?
Yes -> Go to step 5.
No -> Repair or replace the faulty component.
5. Identify the faulty component
The engine components and their installation condition are questionable. Check and correct deficiencies.
If one of the following conditions occurs after starting the engine, eliminate the cause of the problem and perform the idle air learning procedure again from the beginning:
The engine stalls;
Unstable operation at idle speed.
End of check.
I started receiving letters in the mail about the problem of high speeds when starting the engine. Immediately the needle rises to about 3,000 and after a few seconds drops to its normal position. Let's think logically. Why does our engine speed depend? The speed directly depends on the opening angle of the throttle valve. The greater the angle it is open, the higher the engine speed. For those who have a BC, it’s even easier; they can simply look at the IAC readings and determine whether it’s the problem. Those who don’t have a bookmaker will need the help of a friend. You need to put him in the driver's seat, open the hood yourself and watch the metal lever connected to the throttle axis (located in the center of the plastic washer on which the throttle cable is attached). You can watch the video on the page: . This lever is completely connected to the IAC - idle air control. Ask a friend to turn on the ignition. The lever should move to the left, opening the damper slightly to start. The amount of deviation will depend on the engine temperature. If, after starting, the lever deviates even more to the left, thereby opening the damper more, just at 3,000 rpm, and when the speed drops, the lever and the damper close, then the problem is the IAC. The revolutions correspond to the position of the remote control.
Let's look at another option. Let's say our IAC is working properly. What could cause the revs to rise? I often go to forums to see what new problems are popping up on our cars. And there is a wrong opinion there. The question is: “Why low revolutions?” And in the answers they write that they need to look at all the hoses to see if there are any cracks or air leaks. They write correctly, but only for cars with a Mass Air Flow Sensor. This sensor is installed after the air filter and takes into account the air flow passing through it. But the air leak comes after it, and he is not able to determine it. It turns out that more air passes into the engine, and the mixture becomes leaner, which leads to a decrease in speed.
. . With us it’s the other way around. It stands for DBP, and it determines the absolute pressure in the intake manifold. If there is an air leak, it will catch it too. It turns out that the damper lets in its portion of air, and the suction also adds its own. DBP takes everything into account, and the speed increases. And in any case, the injectors inject as much gasoline as is needed for proper engine operation. This is a plus for us. Soon the ECU will understand that the speed is too high and will give a command to the IAC to cover the throttle valve, and everything will settle down. The next time you start it should happen again. Now let's think about where the excess air could come from, other than burst hoses. Three systems come to mind, although even 4.
If the piston is jammed or the spring in the PCV valve (crankcase gas exhaust) is broken, then the air will simply be sucked, bypassing the damper, through a long hose, through the valve cover, through the faulty valve into the air manifold.
. . If the EGR valve of the exhaust gas recirculation system is faulty, then the gases will also flow into the air manifold through a metal tube. It is better to turn off the EGR valve immediately: .
. . If the adsorber purge valve is faulty, then gasoline vapors will also flow through the tube into the manifold.
. . And the last system that is connected to the air manifold is a system for changing its length. To the right of the collector is the actuator itself, black plastic, similar to a mushroom cap. It has a fitting on top, and a black tube is connected to it through a rubber tip. Another tube of this system is connected to the air manifold itself. This mechanism itself has a membrane - a diaphragm, and if it is torn, then air will flow through these tubes into the manifold until the engine exceeds 4,000 rpm. And then it will simply switch to a short collector and block this circle. Tomorrow is Monday, I'll go to work. I think there will be free time to conduct an experiment. I have a lot of plugs on the intake manifold fittings, and even of different diameters. We will simulate air leaks and see how the engine behaves. Then we will know for sure whether our theoretical conclusions and logical chain are correct. OK, see you tomorrow. I think by 10 o’clock in the evening I’ll post the video on both the blog and YouTube.
. . Well, everything is ready.
All car enthusiasts sometimes face such a problem as high idle speed. But, unfortunately, it takes a beginner a significant amount of time to find and fix this problem without visiting a specialized car service center. To do this, you will need a detailed manual that will specifically describe all the necessary actions.
When starting, the engine can reach higher speeds to warm up faster. This manifests itself especially often in winter. But after some time, after reaching the minimum operating temperature, the electronic control unit is activated, which reduces the engine speed to normal. If this does not happen, then it is urgent to look for the reasons causing this problem.
Higher speeds indicate more intense engine operation, which can lead to a wide variety of consequences. Long-term operation may cause the engine temperature to rise significantly, resulting in thermal shock. This will cause problems in the operation of the cylinder block. In addition, most components will experience heavy wear and tear due to unstable engine operation and, as a result, accelerated wear. All this will affect the service life of the engine.
Therefore, it is necessary to immediately figure out what reason caused the increase in speed. There are several of them:
- idle speed sensor
- Problems with throttle angle adjustment
- failure of the engine temperature sensor
- air entering through a damaged intake manifold
- problems with the electronic control unit
Ways to solve problems
Diagnosing this problem requires some knowledge as the process can cause irreparable damage to the engine. Therefore, you must carefully read the operating instructions for this car. It is also important to remember that Chevrolet Niva cars are equipped with injection-type gasoline engines, so increased idle speed on a warm engine is most likely caused by the electronic components of the car.
Checking the idle speed sensor
To do this, the engine warms up to operating temperature. Then just check the sensor using a multimeter. If it malfunctions, you must replace it with a new one.
Throttle position sensor
This component is responsible for the amount of air mixture entering the engine combustion chamber. If the sensor is not configured correctly, the fuel supersaturated with air will detonate more strongly, spinning the engine faster and increasing speed. The sensor can also be checked using a multimeter.
Problems with throttle valve travel.
These problems are similar to the failure of the throttle sensor and lead to the same consequences. Only the main problem here is not electronic - but contamination of the damper itself by oil vapors coming from the crankcase, combustion residues, or due to rare changes of the air filter. If there are traces of contamination, the damper must be cleaned. To do this, you need to completely remove the throttle assembly and either replace it if damaged or clean it using special products. It is important to remember that after cleaning, the throttle valve angle may be incorrectly set due to the so-called “memory effect” in the ECU. In this case, some models will require additional computer diagnostics.
Engine temperature sensor.
This component most often fails because it is constantly exposed to high temperatures. Therefore, in some cases it is better to start looking for problems there. It is also checked using a multimeter. After replacement, the ECU may need to be cleaned for errors.
Damage to the intake manifold.
The collector itself may also fail if the car has a sufficiently long service life. But more often the gasket fails. In this case, excess air is sucked in. To fix the problem, it is necessary to dismantle this part, as well as the units on which the injection elements are located. Before installing the gasket, it is necessary to thoroughly sand the surface of the manifold and clean it of traces of the old gasket. But it is important to remember that the occurrence of this problem is accompanied not only by increased idle speed. Damage to the gasket makes it difficult to start the engine and the speed fluctuates while driving.
As can be seen from practice, there are a very large number of problems that can cause increased idle speed on a warm engine. Therefore, if there are doubts that self-repair will not bring the desired result, it is better to entrust the car to specialists who, with the help of professional equipment, will be able to quickly identify the defect and eliminate it.
As with many other malfunctions, the causes of high engine idle speeds should be sought from simple to complex. In fact, there may be many reasons for these, but among them the most common can be identified:
- high idle speed due to air leaks from the manifold(with subsequent entry into the engine);
- high idle speed due to a leak in the vacuum line;
- high idle speed due to a malfunction of the ignition system engine.
As we can see, these reasons are quite vague, and they should be specified. But the first thing to do is the standard procedure - turn off the car, remove the negative terminal of the battery for 15-20 seconds, then connect it back and check if the problem remains.
High engine idle speed due to air leaks and vacuum line leaks
So, if the cause of high idle speed is excessive air entering the engine, then first of all you should check the throttle cable. Because of it, the damper may remain too open at idle, as a result of which the latter increases. This happens because the “brains” of the engine see that a lot of air (more precisely, oxygen) is entering the manifold, and therefore adjust the fuel supply, increasing it. As a result, the engine speed increases at idle. In this case, cleaning the throttle valve with special chemicals can help.
More air may also enter the collector due to a leak in the air intake system. In this case, you should check all vacuum lines, head breathers and all sections of the air flow line into the engine for air leaks. Listen for hissing sounds, which can be a key indicator of vacuum leaks and air leaks.
Increased idle speed due to problems in the ignition system
In this case, the reason lies in one of the parts of the ignition system - also a fairly common cause of problems with speed. Here you should check and, if necessary, replace the distributor cap, ignition wires or even spark plugs.
Other causes of high idle speed and solutions:
- Idle speed sensor. In principle, this malfunction should be included in the list of common...
- Fuel pressure control may operate at too low pressure. Check the fuel pressure using a special fuel pressure gauge. Replace the fuel pressure regulator if necessary (not a DIY job for many drivers).
- Incorrectly installed or knocked down ignition timing(in this case, the idle speed usually does not increase much).
- The reason may be malfunction in the computerized control system engine. Errors should be read using a scan tool to identify the problem.
- Generator also sometimes causes high idle speeds. If it's not working properly and isn't generating enough current, the motor will try to spin it even harder to balance the voltage.
- If you know what it looks like and where it is PCV valve and its hose, then inspect them. Using pliers, pinch the hose of this valve. The engine speed should decrease slightly. If this does not happen, then the cause of the increased engine speed is a faulty valve - it needs to be replaced.
- In rare cases, engine overheating or a faulty engine temperature sensor can also cause high idle speeds.
