What is the normal idle speed for a vehicle?
3 Answers
Vehicle idle speed is considered normal between 550 to 800 revolutions per minute (RPM). The minimum rotational speed required to maintain stable engine operation is referred to as idle speed, which is one of the five fundamental operating conditions of an engine. The idle speed can be adjusted by modifying the throttle opening size and the idle fuel supply quantity. Engine types include: 1. Classified by fuel type: gasoline engines and diesel engines; 2. Classified by stroke: four-stroke internal combustion engines and two-stroke internal combustion engines; 3. Classified by cooling method: water-cooled engines and air-cooled engines; 4. Classified by cylinder arrangement: single-cylinder engines and twin-cylinder engines; 5. Classified by intake system: naturally aspirated engines, turbocharged engines, and supercharged engines.
Under normal circumstances, I personally believe that an idle speed of 700 to 900 RPM is within the standard range. My old car maintains a stable idle at around 800 RPM, which feels most comfortable; during cold starts, it rises to 1200 RPM but drops back down after a few minutes. If the idle is unstable, it might be due to a dirty throttle body or spark plug issues—I cleaned my throttle body myself, and it improved. It's also normal for the idle to be slightly higher when the AC is on in summer, but it's best not to let the engine idle for too long, as it wastes fuel and harms the engine. In general, keeping the idle between 600 and 1000 RPM is fine, but always refer to your vehicle's manual for specific guidelines.
From the perspective of engine tuning, the normal idle speed for most cars falls within the range of 600 to 1000 RPM. I've noticed that newer turbocharged engines may idle as low as 650 RPM, while older naturally aspirated engines often idle above 900 RPM. The ECU controls the RPM and automatically adjusts it based on factors like AC activation and battery load. If the idle speed is too high or too low—for instance, stalling below 500 RPM or exceeding 1200 RPM, which may indicate fuel injection issues—it's necessary to check the oxygen sensor or air filter. In daily driving, just pay attention to the dashboard warnings to ensure a stable idle speed.
