The idle mode (XX) is the mode of operation of the internal combustion engine, which is necessary to maintain the process of fuel combustion in the cylinders at a minimum level, that is, that the engine continues to work and is not stalled. On different engines, idle speed may vary, and also depend on the temperature of the engine. In the case of an increase in the indicated revolutions of the XX engine starts to consume more fuel, the exhaust in this mode becomes more toxic. Lower idling 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 idle engine speeds, why high idle speed on a warm engine is found on many cars, and also consider the main ways to diagnose this malfunction.
High engine idle: injector
Turnover and motor operation on the twentieth in fact means that air is supplied to the engine bypassing the throttle. In other words, at idle, said damper is closed. Note that, normally, the idle speed for different units is about 650-950 rpm. Parallel to this, a frequent malfunction is that on a warmed-up engine the twentieth revolutions are kept at about 1,500 rpm and higher. This indicator is a sign of a malfunction that should be addressed.
It should also be noted that when the idle speed “floats”, that is, for example, they increase to 1800 rpm, after which they decrease to 750 and increase again. Very often, increased revolutions of the twentieth and floating revolutions are the result of the same breakdowns. Let’s take a look at the petrol unit with an injector as an example. In such an engine, the engine speed depends on the amount of intake air. It turns out that the stronger the throttle opens, the greater the amount of air enters the intake manifold. Then the computer determines the amount of incoming air, in parallel takes into account the opening angle of the throttle (throttle position) and a number of other parameters, after which it supplies the corresponding amount of gasoline.
Another case is when the engine keeps idle at about 1500-1900 rpm, while running smoothly, the speed does not float. In this case, it can be assumed that the injector delivers so much fuel in the XX mode that it is enough to operate at such high speeds. In other words, there is an overspending of fuel. These features may be characteristic of some engines and may not be present on others, since there is a dependence on the device for a particular injection system (units with an air meter, motors with a pressure sensor in the intake manifold). Obviously, air leaks are a common cause of increasing engine rpm or floating rpm on the twentieth.
Video: Trimmer Does Not Hold Idle
Now let’s figure out where the excess air can enter the inlet. There are four main areas to look for a problem:
- throttle body;
- channel XX;
- a device for maintaining the “warm-up” speed;
- servomotor of forced increase of turns XX;
As for the first case, the throttle is controlled by the accelerator pedal. The engine should idle without pressing the accelerator. It should be borne in mind that on many cars the gas pedal is mechanical, that is, it is connected to the flap opening mechanism with a conventional cable. If this cable is soured, twisted or pulled, and there are also problems with the mechanism itself, then there may be a banal effect of pressing the gas pedal. In this case, the engine will keep increased speed, as the ECU believes that the driver presses on the accelerator and the damper is slightly ajar.
In the second case, excess air can pass through the idle channel. Such a channel is available on the vast majority of injection ICE. The specified air channel bypasses the throttle and is called the idle channel. In the implementation of the circuit there is a special adjusting screw. Using this screw, you can change the cross section of the channel, increasing or decreasing the amount of air entering the motor and adjusting the RPM.
As a result, the computer 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 computer receives readings from the temperature sensor and enriches the fuel mixture. Problems with speed can occur both as a result of the failure of this device, and after malfunctions of the temperature sensor.
The list is completed by a special servo system. the idle speed regulator, which is installed in a separate air channel. This solution is able to forcibly increase idle speed. In various schemes, it can be an electric motor, a solenoid, a variant of an electromagnetic valve, etc. The main task of such a regulator is to ensure a smooth transition of the engine to XX mode after releasing the gas pedal. In other words, the engine does not sharply slow down after closing the throttle, but gradually. Another function of the device is to increase idle speed at the time of engine start, and then gradually decrease them to the necessary ones. Also, the controller increases speed after increasing the load on the engine in idle mode (turning on the climate control, heating the seats or mirrors, high or low beam headlights, parking lights, etc.). The failure of this device will naturally lead to an increase or swimming speed in idle mode.
Increased RPM on engines with a carburetor
At the very beginning, we note that the increase in twentieth revolutions on carburetor engines is often associated with the dosing device itself. If high idle engine speeds are noted in the case of a carburetor engine, then there may be several reasons.
- The first reason is knocked idle adjustment. Such adjustment is carried out with the help of an adjusting screw, which allows to enrich or deplete the mixture. To solve the problem, the idle speed on the carburetor should be correctly adjusted.
- You should also pay attention to the fact that the air damper may not fully open on carburetor cars.
- Another place to pay attention to is the shutter of the first chamber in the carburetor. The specified damper may not close completely due to defects in the damper itself or incorrectly adjusted actuator.
- Finally, we add that in the float chamber of the carburetor there may be a noticeable increase in fuel level, which also leads to an increase in idle speed.
What is the result
It should be noted that the problem of idling on an engine with an injector is diagnosed by checking the main systems that are responsible for the intake of air into the internal combustion engine, as well as changing the composition of the mixture taking into account the amount of incoming air. It turns out, it should be borne in mind that the failure of individual ECM sensors can lead to an increase or floating speed of the twentieth.