Why does a diesel car have unstable idle speed with fluctuations?
1 Answers
Unstable idle speed in a car is mainly manifested by the fluctuation of the tachometer needle and unstable pointing during idling. Unstable idle speed can be considered one of the most common engine faults, which can range from minor to severe. It is often accompanied by idle vibration. The following are the reasons for unstable idle speed: 1. Oil accumulation and carbon deposits in the throttle body, and dirty intake passages: Blocked intake passages can cause idle speed fluctuations, while carbon deposits or oil in the throttle body are the most common causes of unstable idle speed. Carbon deposits in the throttle body can affect its opening, thereby influencing the intake air volume, causing the engine speed to fluctuate significantly and become very unstable after a cold start, accompanied by strong vibrations. 2. Fuel system blockages represented by the fuel injector and intake pipe faults: These can lead to insufficient fuel supply pressure, poor fuel atomization, an imbalanced air-fuel mixture ratio, and incomplete combustion, resulting in related fault phenomena. If there is an air leak in the intake pipe, it can affect the accuracy of the air flow meter's data, causing the ECU to inaccurately control the intake air volume, which also leads to an imbalanced air-fuel mixture ratio and unstable engine idle speed.
