What is the normal idle speed when starting a car?
2 Answers
For a car, the normal idle speed when starting is between 700 to 800 RPM. If it's too low, the engine is prone to shaking, and if it's too high, it results in increased fuel consumption. Idle speed refers to the engine's RPM when the throttle pedal is completely released during operation. The idle speed can be adjusted by modifying the throttle opening size, and the optimal idle speed is the lowest RPM at which the engine does not shake. The hazards of unstable car idle speed are: 1. If the car's idle speed is too high, check whether the intake manifold is loose or leaking, as it will significantly increase fuel costs and accelerate engine carbon buildup; 2. If the car's idle speed is too low, there is a safety risk of stalling while driving; 3. If the car's idle speed fluctuates, it might be due to spark plugs or high voltage not working properly, causing the engine pistons to malfunction and resulting in severe shaking.
What is the normal idle speed after starting a car? It depends on the specific situation, but most gasoline cars have a normal idle speed of around 700 to 900 RPM after warming up. From my experience, newer cars tend to be more stable, usually around 750 RPM. During a cold start, the idle speed might be higher, such as above 1000 RPM, because the engine needs to warm up quickly; it will gradually drop after driving for two or three minutes. If the idle speed is unstable or fluctuates too much, there might be issues like a dirty air filter, worn spark plugs, or a clogged throttle. I recommend regularly checking the tachometer on the dashboard—if it stays stable between 700-900 RPM, it's fine. Additionally, the owner's manual provides specific values for reference, and different models, such as automatic and manual transmissions, may have slight variations. Diesel engines might have slightly higher idle speeds. If the idle speed is consistently too high or too low, getting it checked early can prevent more serious issues and save you from costly repairs.
