Do automatic transmission cars have idle speed?
3 Answers
Automatic transmission cars do have idle speed, which is one of the five basic operating conditions of an engine, representing a working state when the car engine is running without load. Idle speed refers to the engine running without any load, only overcoming the internal friction resistance of its components without delivering power output. In other words, when the engine is running and the accelerator pedal is released, it enters idle speed state. The idle speed can be adjusted by modifying the throttle opening size and idle fuel supply quantity. As long as the engine doesn't vibrate within the idle speed range and maintains good acceleration performance, the setting is appropriate. It's important to note that when adjusting idle speed, the RPM should not fluctuate excessively, as this could cause wear to the engine.
Automatic transmission cars certainly have idle speed. I remember the first time I drove my friend's automatic car. When I shifted to P (Park) and stopped, the engine was still running quietly, with the tachometer resting at its lowest position. This is the idle state, where the engine keeps running without load to prevent stalling. Whether the car is warm or cold-started, idle is always present, especially during traffic jams or when stopped at traffic lights, allowing the air conditioning and audio system to continue functioning. However, one thing to note is that in D (Drive) gear, idle speed can cause the car to creep forward slowly, so you must keep your foot on the brake. If the idle becomes unstable—for example, if the RPM fluctuates up and down—it might be due to carbon buildup or sensor issues, and you should get it serviced. Overall, idle speed makes driving smoother, especially in stop-and-go urban conditions.
When it comes to automatic transmission idling, I always pay close attention to these details. The car engine definitely has an idling function in automatic mode. When the vehicle is stationary in P or N gear, the ECU controls the throttle and fuel injection system to maintain low RPM and prevent stalling. The idling speed typically ranges between 600 to 800 RPM, providing stable power supply to various electronic devices such as the air conditioning compressor. However, idling consumes quite a bit of fuel, averaging about 1 liter of gasoline per hour, and also increases exhaust emissions. Therefore, I recommend shifting to N gear during prolonged waits or utilizing the auto start-stop feature in newer vehicles to temporarily shut it off. Occasional abnormal idling, such as shaking or noise, is mostly caused by a dirty air filter or aging spark plugs, which need prompt attention. This mechanism is ingeniously designed yet often overlooked by people.
