What is the appropriate idle speed?
2 Answers
Normally, it is around 700-800 RPM. If it's too low, the engine may shake; if it's too high, fuel consumption increases. As long as there is no shaking, design engineers prefer to keep it as low as possible to save fuel. Unstable idle speed in cars can lead to the following hazards: 1. High idle speed: Check if the intake manifold is loose or leaking, as this can significantly increase fuel costs and also lead to more engine carbon deposits. 2. Low idle speed: While driving, there is a risk of the engine stalling at any time, posing a safety hazard. 3. Fluctuating idle speed: This could be due to non-functioning spark plugs or ignition coils, causing the engine pistons to malfunction and resulting in severe shaking.
I've driven various cars, and the ideal idle speed is usually around 700 RPM. This depends on the engine type and environment—gasoline cars typically fluctuate between 600 and 800 RPM, and may rise to 1000 RPM during a cold start but drop back after a few minutes. If the air conditioning or headlights are on, the RPM might jump to 800, which is normal. Sensors control the idle speed, and maintaining stability is crucial; too low, like below 500 RPM, may cause the car to shake or stall, while too high, like above 900 RPM, can increase fuel consumption or even damage the engine. Regularly checking the tachometer can help you spot abnormalities, such as a dirty air filter or vacuum leaks causing issues. New cars usually default to 700 RPM from the factory—if the idle speed is consistently unstable, promptly visit a repair shop to check the throttle and spark plugs to avoid safety risks. In short, keeping it within this range ensures efficiency and safety.
