What is the idle speed?
3 Answers
When the engine is running, if the throttle pedal is completely released, the engine will be in an idle state. Idle principle: The phenomenon of idling is that the car remains stationary while the engine is running—burning fuel in vain, which is indeed a waste! At this time, the mechanical energy generated by gasoline combustion is consumed by the friction of internal parts. Idle application: On cold mornings, it is necessary to warm up the car. The colder the weather, the longer the time required. To speed up the process, impatient people may pull the throttle hard or temporarily increase the idle speed. This does make the process faster, but at this time, because the cylinder block is too cold, some gasoline droplets adhering to the cylinder wall dilute the oil on the cylinder wall, thinning the oil film formed between the piston and the cylinder wall. Meanwhile, the excessively high speed exacerbates the friction.
Idle speed usually refers to the engine's RPM when it's running without load, typically ranging between 600 to 1000 RPM depending on the vehicle model and conditions. Based on my years of driving experience, idle speed fluctuates with temperature. For instance, during cold winter starts, it can surge above 1000 RPM for a few minutes before stabilizing around 700 RPM. In summer with AC on, it may rise to 800 RPM, which affects power output. If the idle becomes unstable—with the tachometer needle fluctuating—it's a serious warning sign, likely indicating spark plug carbon buildup or valve issues that require immediate repair. At traffic lights, maintaining around 750 RPM is most fuel-efficient. I always prioritize keeping the engine smooth and avoid prolonged idling to save fuel—after all, who doesn't want to cut costs while being eco-friendly?
The idle speed typically ranges between 600 to 1000 RPM, but this figure isn't fixed and varies by engine type. As someone who tinkers with car repairs, I know gasoline engines usually idle smoothly at 750 RPM, while diesel engines may hover around 900 RPM. The ECU system monitors temperature sensors and air flow meters to fine-tune idle speed automatically, preventing engine shudder. If the RPM abnormally spikes (e.g., to 1200 RPM) or drops (say, to 500 RPM), it might indicate a dirty idle control valve or throttle body needing cleaning. Checking is simple—just plug in an OBD scanner to read the data. Monitoring startup behavior helps catch major issues early; for instance, hard starting often signals abnormal idle speed.
