What is the appropriate idle speed for a car?
2 Answers
An idle speed of 700 to 900 RPM is generally considered appropriate for a car. Idling refers to the operation of the engine under no load, where it only needs to overcome the internal friction resistance of its components without delivering any external power, maintaining the minimum stable operating speed of the engine. The idle speed of a car is not a measure of velocity but rather an operational state. When the engine runs without any load, it is referred to as idling. If the accelerator pedal is completely released while the engine is running, the engine enters the idle state, and the rotational speed at this time is called the idle speed. The idle speed can be adjusted by modifying the throttle opening size, among other methods. The optimal idle speed is the lowest RPM at which the engine does not vibrate.
Having driven for over 20 years, I find that an idle speed between 600 to 900 RPM is generally appropriate, as most vehicle models are set within this range. If the idle speed is too low—below 500 RPM—the car is prone to stalling, especially during cold starts or when the air conditioning is on. Conversely, if it's too high—exceeding 1000 RPM—it unnecessarily wastes fuel, increases consumption, and may cause noticeable vibrations. It's normal for the idle speed to be higher during cold starts in winter, but it should stabilize after the engine warms up. Unstable idle speeds might indicate a dirty air filter or throttle valve issues, which can often be resolved with regular cleaning. I recommend new car owners consult their manual for specific idle speed values rather than attempting to adjust the settings themselves, as improper adjustments could harm the engine. Before long trips, using a simple diagnostic tool to check the idle speed can save a lot of hassle.
