For a stereotyped car, the idle speed of the engine is related to the coolant temperature, battery voltage, whether it is equipped with an air conditioner, etc., and has nothing to do with the engine displacement. It is set by the car factory according to the needs of the vehicle performance, and is controlled by the engine computer closed-loop.
Let’s take a look at how a car with an electronic throttle controls the idle speed? The picture below is an electronic throttle valve. The opening of the throttle valve is driven by a motor with its own. When idling, the engine computer will give the electronic throttle valve an opening according to the target idle speed value calculated by it. Then, according to the comparison between the actual measured engine speed value and the target idle speed value, it is decided whether to open it up or close it down. At idle speed, the response of engine speed to the change of intake air volume is relatively slow, the throttle valve opening finds the basic range of engine idle speed, and the stability of idle speed is solved by adjusting the ignition angle.
The actual idle speed should be stable within plus or minus 50 revolutions of the target speed.
Let’s see how the mechanical throttle adjusts the idle speed? The valve opening of the mechanical throttle is controlled by the throttle cable. There is a bypass hole on the throttle body. A motor that adjusts the cross-sectional area of the air passage is installed on this bypass channel. This is what we often call the idle motor.
The closed-loop adjustment algorithm of idle speed is similar to that of the electronic throttle valve, except that the idle speed motor is used to control the intake air volume at idle speed.
So for a car in use, the idle speed value when the car is hot is certain, such as 700RPM, and the idle speed is stable at Anything between 650 and 750RPM is normal. If one day, the hot car idles to 800 rpm, this is a malfunction.
When the coolant temperature is low, the idle speed should be higher, in order to warm up the car as soon as possible.
When the battery voltage is insufficient, the idle speed should be higher.
After the air conditioner is installed, the idle speed is generally increased by 50-100RPM.
When the cooling fan is running, the idle speed will also increase.
Please tell me under what circumstances does the idling speed of your car increase?