What is the normal engine idle speed?

[DiLyla]

An engine idle speed around 850 RPM is considered normal. If the engine is cold, a speed not exceeding 1200 RPM is reasonable. Generally, smaller-displacement cars have an idle speed close to 700 RPM, while larger-displacement vehicles approach 1000 RPM. Below is an extended introduction to car idle speed: 1. A car's idle refers to an operating condition. When the engine runs without load, it is called idling, meaning the car is in neutral gear. The engine speed during idling is called the idle speed. The idle speed can be adjusted by modifying the throttle opening size. Idling means the engine is "running without doing work." 2. When the engine is running, if the accelerator pedal is fully released, the engine enters idle mode. When adjusting the idle speed, the RPM should not fluctuate abruptly, as this may cause premature engine wear. It is best to have it adjusted at an automotive repair facility. 3. When starting the engine in a parked state, the minimum stable operating speed is called parking idle (the process of transitioning from a cold engine idle state to a normal operating temperature idle state is called warming up or heating the engine).

[OMartin]

I've been driving a taxi for twenty years and have handled all kinds of cars. It's normal for the RPM to be around 1200 when starting a cold engine, and it should stabilize between 750-850 RPM once the engine warms up. Turning on the AC usually adds about 100 RPM, and it's common for the RPM to drop by another 50 when shifting to D and pressing the brake. If the needle jumps wildly between 500 and 1200 RPM, or the car shakes like a massage chair, you should immediately check the spark plugs or carbon buildup. Older German cars generally have lower RPMs, while Japanese cars run slightly higher—this is due to tuning differences. I remember a passenger once said his Camry always idled at 600 RPM, but a dealership check revealed it was just a gauge error.

[DelStephen]

Last time when helping my daughter look for a used Fit, I did some research: For small-displacement four-cylinder cars, an ideal normal idle speed is around 700±50 RPM. Turbocharged cars might be about 100 RPM higher, since they need to leave some margin for the turbo. A mechanic taught me a trick—listening to the sound is more accurate than watching the gauge. If the engine sound is uniform like a buzz, it's healthy; if there's metallic knocking or fluctuating RPMs, chances are the throttle body is dirty. Nowadays, new energy vehicles are more complex—hybrid engines' RPMs can suddenly change during start-stop, but as long as it stabilizes at a fixed value after stopping, it's fine.

[OLola]

A friend who has modified racing cars told me that idle tuning depends on the purpose. For daily driving, 800 RPM is the most balanced, saving fuel and preventing shaking. If you've installed a high-lift camshaft, you need to adjust it to 1000 RPM to avoid stalling. During monitoring, ensure the coolant temperature reaches 90°C and turn off all electrical loads. Observe the tachometer for at least 3 minutes—if the needle fluctuates more than ±30 RPM, check the vacuum lines. A faulty knock sensor can also cause idle fluctuations, which is particularly common in classic cars.