What Causes Severe Idle Vibration in Cars?

1 Answers
DeMaria
07/29/25 11:01am
Reasons for severe idle vibration in cars: 1. Leakage in the intake manifold or various valves, causing abnormal engine combustion; 2. Excessive carbon buildup in the throttle body and intake passages, leading to overly rich or lean air-fuel mixture and resulting in abnormal combustion; 3. Faulty idle air control components, which can cause inaccurate idle air control and result in unstable idle speed. Taking excessive carbon buildup in the throttle body and intake passages as an example, when there is too much carbon deposit inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits, causing the air-fuel mixture to be too lean during cold starts and making it difficult to start. In this situation, the engine will only start easily once the carbon deposits have absorbed enough gasoline to become saturated. After starting, the gasoline adsorbed on the carbon deposits will be drawn into the combustion chamber by the engine's vacuum suction force, making the air-fuel mixture too rich. This alternation between lean and rich combustible mixtures causes idle vibration after a cold start.
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