What are the main reasons for slow idle speed reduction?
2 Answers
The main reasons for slow idle speed reduction include malfunction of the idle speed motor; excessive valve clearance; excessive engine carbon deposits. The solution is to clean the engine carbon deposits. Introduction to car idle speed is as follows: Introduction to idle speed: It refers to the operation of the car's engine without load, with the engine working in neutral gear. Under normal circumstances, an engine with good working performance has an idle speed generally between 550-800 rpm; Idle speed adjustment: The vehicle's idle speed can be adjusted by the throttle opening size, idle fuel supply, etc. If the vehicle does not shake within the idle speed range, the idle speed is optimal. Warm-up refers to the process of the engine transitioning from cold idle speed to the idle speed state at normal operating temperature.
Last time I encountered a situation where the RPM dropped very slowly, so I first checked the throttle body. Turns out, carbon buildup had clogged the opening, making the throttle pedal feel sticky when pressed. The mechanic said this issue is more noticeable in cold weather, especially for cars that haven't been driven for several days. The air filter also needs attention—like mine, which often runs on dirt roads in the suburbs. If the filter is clogged, restricted airflow can prevent the RPM from dropping. Dirty sensors can also trick the computer, and when the idle control motor gets stuck, you can even hear a buzzing noise. Additionally, older cars need special attention to vacuum leaks. Spraying carb cleaner near the pipe openings and hearing the engine shake indicates a leak. After cleaning the throttle body, the idle stabilized immediately, and the car felt five years younger.
