What is the cause of unstable idle speed?

The reasons for unstable idle speed are as follows: 1. Throttle oil storage and throttle carbon deposit, air intake is too dirty. Due to carbon deposition, the throttle will affect the opening and air intake, which will make the engine speed fluctuate after the car is started, which is very unstable and accompanied by strong jitter. The throttle valve has serious oil storage or carbon deposition, including unclean air intake, which makes it difficult to start the car in cold weather. 2. Spark plugs caused by individual spark plug failures are too weak. The spark plugs on individual cylinders are weak, which will affect the performance of the car. Spark plug failure will lead to "fire" symptoms of the car, but spark plug failure of individual cylinders will lead to unstable idle speed symptoms. 3. The oil path represented by the choke is blocked and the air inlet pipe is faulty. When the fuel passage represented by the fuel nozzle is blocked, it will cause insufficient fuel supply pressure, poor fuel atomization, unbalanced mixing ratio and incomplete combustion, which will lead to related failures. If the intake pipe leaks air, it will affect the real data reflected by the air flow meter, resulting in inaccurate control of intake air volume by ECU, unbalanced mixing ratio and unstable engine idle speed. 4. Related sensor failure. The failure of related sensors will make ECU unable to control the correct air-fuel ratio, such as water temperature sensor, oxygen sensor, throttle position sensor and other common failures. , the relevant sensors need to be replaced.