What is the normal idle speed for an engine?
2 Answers
For vehicle diesel engines, the normal idle speed ranges from 500 to 800 RPM, while for gasoline engines, it ranges from 700 to 1000 RPM. The engine speed at idle is referred to as the idle speed, which is the minimum speed required to keep the engine running normally without any load. The idle speed of the same vehicle differs between cold and warm conditions. The engine's computer controls the high idle speed when the engine is cold, aiming to rapidly increase the water temperature to reach the normal operating temperature, reduce engine wear, and minimize harmful emissions. As the water temperature rises, the idle speed gradually decreases and eventually returns to the normal idle speed when the engine is warm.
As a seasoned driver with over a decade of experience, I can tell you that an ideal engine idle speed typically ranges between 700 to 900 RPM. When the engine is cold upon startup, it's normal for the idle to temporarily rise to around 1000 RPM before settling back to standard values after warming up. If the idle drops too low (below 600 RPM), the vehicle may shake or even stall - which is particularly dangerous at traffic lights. Conversely, sustained high idle (above 1000 RPM) often indicates severe carbon buildup or sensor issues, increasing fuel consumption and emissions. I recall when my car had unstable idle, cleaning the throttle body immediately improved the situation. Avoid prolonged idling as it wastes fuel and harms the engine. Variations exist between models - diesel engines normally idle higher, and manual/automatic transmissions behave differently. Regular maintenance like oil changes and air filter replacements prevents idle issues and ensures driving safety.
