What is the normal idle speed for a BMW 3 Series?
2 Answers
Generally, the normal idle speed for sedans is between 700-900 RPM, and it's acceptable as long as it falls within this range. When the air conditioning is turned on, the idle speed increases to around 800-850 RPM. The hazards of idling and methods to reduce idling fuel consumption are as follows: Hazards of vehicle idling: During idling, the engine intake air volume is low, requiring a richer air-fuel mixture to maintain operation, resulting in higher fuel consumption. Additionally, prolonged idling leads to incomplete fuel combustion, which can easily cause carbon buildup in the engine. Methods to reduce idling fuel consumption: Currently, vehicles equipped with automatic start-stop functionality can effectively reduce fuel consumption during idling. When waiting at traffic lights, the vehicle can automatically shut off the engine to save fuel. To restart the engine, simply lightly press the accelerator pedal, and the engine will automatically ignite.
I've been driving a BMW 3 Series for several years and usually notice the idle speed is normally between 650 to 850 RPM. It's a bit higher during cold starts, around 750 to 900 RPM, but stabilizes below 700 RPM after driving a few kilometers when the engine warms up. When the air conditioning is on, the idle speed might increase to 750-850 RPM, which is completely normal. My own 330i typically shows an idle speed just over 750 RPM on the gauge, and it's quite smooth. If the idle speed consistently jumps to 1000 RPM or drops to 500 RPM, the car shakes noticeably—this could indicate severe carbon buildup, a dirty throttle body, or worn-out spark plugs, and it's time for cleaning or part replacement. Last month, my car had unstable idle speed, and after inspection, it turned out the air filter was clogged. Replacing it immediately improved the situation. Overall, BMW's idle speed control is very precise, so there's no need to worry too much, but regular maintenance and checks can prevent major issues, especially for older models.
