What is the reason for the unstable idle speed of the engine?

Strictly speaking, unstable idle speed generally refers to the jitter or severe jitter when the idle speed exceeds the expected value of 20r/min. Don't be afraid of the car idling unsteadily. Most of them are caused by these four reasons, such as the accumulation of oil and carbon in the throttle, unclean intake and so on. It is right to prescribe the right medicine.

1. Throttle oil accumulation and throttle carbon accumulation. Dirty and blocked air intake will cause idling delay, and carbon deposition or engine oil on throttle is the most common cause of idling instability. The carbon deposit on the throttle will affect the opening and air intake, making the engine speed fluctuate after the cold start of the car, which is very unstable and accompanied by strong jitter. Serious oil or carbon accumulation in the throttle, including unclean air intake, makes it difficult to start the car in cold weather. The throttle is dirty and needs to be cleaned. Cleaning the throttle itself is also a daily maintenance item. Second, the spark plug caused by individual spark plug failures is too weak, and the spark plug will also deposit carbon, so the activity of the spark plug can be restored by cleaning. However, the service life of some spark plugs is approaching, and the performance will also decline. The weak spark of the spark plug on a single cylinder will affect the performance of the car. We know that the spark plug failure will cause the car "fire" symptoms, but the slight failure of the spark plug on individual cylinders will cause the idling instability symptoms. Therefore, cleaning or replacing the spark plug is also an option to solve the problem when the idle speed of the car is unstable. Three. Oil blockage and intake pipe failure represented by injector When the oil blockage represented by injector, it will cause insufficient oil supply pressure and poor fuel atomization, resulting in unbalanced mixing ratio and incomplete combustion, thus causing related failures. If the intake pipe leaks, it will affect the real data reflected by the air flow meter, resulting in inaccurate control of intake by ECU, unbalanced mixing ratio and unstable engine idle speed. Cleaning the oil circuit is also a maintenance project, which we call engine health care. There is something wrong with the oil circuit, the emission exceeds the standard, and the annual inspection of the vehicle is unqualified. 4. Related sensor failures Related sensor failures will make ECU unable to control the correct air-fuel ratio, such as water temperature sensors, oxygen sensors, throttle position sensors and other common failures. Generally, the water temperature sensor is installed on the water jacket of the engine cylinder block or cylinder head, which directly contacts with antifreeze to measure the temperature and send relevant reference data to ECU. Once the water temperature sensor fails, the car will have faults such as increased fuel consumption, unstable idle speed and abnormal speed. On the other hand, the failure of throttle position sensor and front oxygen sensor will lead to air-fuel ratio error, which will lead to incomplete combustion of mixed gas and related failures. In this case, the relevant sensors need to be replaced.

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