What Causes Fluctuating Idle Speed in Cars?

[Leanne]

The reasons for fluctuating idle speed in cars are as follows: Excessive accumulated dirt: When too much dirt accumulates in the throttle and surrounding intake passages, it changes the cross-sectional area of the air channel. This also prevents the control unit from accurately controlling the intake air volume during idle, resulting in excessively rich or lean air-fuel mixtures and abnormal combustion conditions. Severe engine carbon buildup: When there is excessive carbon buildup inside the car's engine, the gasoline injected by the cold start injector gets absorbed by the carbon deposits, causing the air-fuel mixture to become too lean. During startup, this makes the engine's air-fuel mixture unstable, leading to irregular idle speed that fluctuates up and down.