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What Are the Causes of Low and Unstable Car Idle Speed?

1 Answers

DelHaven

07/29/25 10:32pm

The causes of low and unstable car idle speed are: 1. Severe engine carbon deposits, excessive carbon buildup in the throttle body and intake passages; 2. Faulty fuel pressure regulator; 3. Clogged fuel injectors, clogged fuel filter; 4. Carbon deposits on spark plugs, incorrect spark plug gap; 5. Excessive resistance in high-voltage wires. Excessive carbon deposits and dirt in the throttle body and surrounding intake passages change the cross-sectional area of the air passages, making it difficult for the control unit to precisely control the idle air intake. This results in an overly rich or lean air-fuel mixture, leading to abnormal combustion. Spark plugs can also accumulate carbon deposits, which can be cleaned to restore their activity. However, some spark plugs nearing the end of their service life may experience reduced performance. Weak sparks from individual spark plugs can affect the car's performance. Faulty spark plugs can cause misfiring symptoms, but minor faults in individual spark plugs may result in unstable idle speed.

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