What is the normal idle speed of a car?
3 Answers
Car idle speed is generally 700-800 RPM, depending on the vehicle model. The hazards and causes of abnormal idle speed are as follows: Hazards of abnormal idle speed: Excessively high idle speed increases fuel consumption, accelerates carbon buildup in the engine, and intensifies engine wear. Excessively low idle speed may cause engine shaking and pose a safety hazard of stalling while driving. Causes of abnormal idle speed: Reasons for abnormal engine idle speed include malfunctioning spark plugs or ignition coils, excessive carbon buildup in the throttle body, loose or leaking intake manifold, improper choke adjustment, fuel injector failure, etc.
After a normal car starts, the idle speed is generally around 700 to 900 RPM. From driving different models, I've noticed that small-displacement naturally aspirated engines tend to idle lower. For example, my old Nissan Sylphy idles at about 1200 RPM when cold but stabilizes around 750 RPM once warmed up. Turbocharged cars, like my friend's Volkswagen Sagitar, usually maintain an idle speed just over 800 RPM. In winter, when temperatures are low, the idle speed may be higher at startup as the engine warms up quickly, but it drops back down after a couple of minutes. If you notice the tachometer fluctuating at a red light or excessive vibration, it might indicate a dirty throttle body or worn spark plugs, and it's time for a check-up.
I was often asked about idle speed issues when repairing cars. Actually, each car model has different tuning—Japanese cars usually idle steadily at around 700 RPM, German cars at about 800 RPM, and American cars might be slightly higher. The key is to focus on stability: the needle should stay steady without jumping after the engine warms up. If you turn on the AC or shift to D while braking, the RPM might drop by 100 but should recover quickly. There's an old trick among experienced drivers: balance a coin on the steering wheel—if the car's idle is stable, the coin will stay upright. If the RPM suddenly rises to 1500 and won't come down, it's likely due to a stuck idle control valve or a vacuum leak.
