What is the appropriate idle speed for an automatic transmission sedan?

[ElizaLee]

Automatic transmission sedans typically have an appropriate idle speed between 5 to 10 kilometers per hour. Idle state refers to an operating condition where the engine is running without load - when the accelerator pedal is fully released during engine operation, the engine enters idle state. The vehicle's idle speed may vary slightly depending on different engine types and models. During cold starts, the car's idle speed will be higher as engine wear is more severe when operating at low temperatures. When the engine control unit detects low engine temperature, it increases idle speed to help the engine reach optimal operating temperature faster and adjust to normal working conditions, thereby avoiding excessive wear. In idle state, the engine only needs to overcome internal component friction resistance without delivering output power.

[BeckettFitz]

Speaking of automatic transmission idling, I've seen plenty in over a decade of car repairs. After proper warm-up, maintaining 600-900 RPM is ideal - Japanese cars often idle around 700 RPM while German models may run slightly lower. During cold starts, it'll spike to 1200-1500 RPM before gradually dropping as the coolant temperature rises. A 100 RPM increase with AC on is normal since the compressor runs on engine power. Watch out for erratic tachometer fluctuations - that usually means carbon buildup clogging the throttle body or a faulty oxygen sensor. Too low idle makes the car vibrate like a massage chair, while excessive RPM wastes fuel and damages the catalytic converter over time. Simple self-check: observe if the tachometer stabilizes after restarting a warmed-up engine.

[SanAlexis]

My automatic transmission car has been running for over five years, and I keep an eye on the dashboard during my daily commute. I've noticed that during a cold start, the RPM can reach 1400, but it drops to around 800 after three minutes. In summer, when the air conditioning is on and waiting at a red light, the RPM stays around 900 due to the compressor consuming power. The most comfortable idle speed is 700 RPM, where the car runs smoothly and saves fuel. If the RPM suddenly drops below 500, you can even feel the steering wheel vibrate, which is a sign to check the spark plugs and fuel injectors. Be cautious if the idle speed remains high after a long trip, as it might indicate an air intake system leak. Remember, idle speed isn't fixed; transmission fluid temperature and battery voltage can cause fluctuations.

[LeColin]

For car enthusiasts, idle speed is like the heartbeat of the engine. For automatic transmission vehicles, a warm idle speed of 700 RPM is a critical threshold. Four-cylinder engines typically stabilize at this figure, while three-cylinder engines need to be set slightly higher to prevent vibration. The high idle speed during cold starts is pre-programmed by the ECU to rapidly heat up the catalytic converter. Modified vehicles with aftermarket intake or exhaust systems require extra attention, as idle speeds in winter temperatures below zero may be 200 RPM higher than normal. If abnormal idle speed is detected, don't delay repairs – prolonged sensor malfunctions can damage piston rings. Newer models feature active idle control that automatically shuts off and restarts the engine at red lights, actually improving fuel efficiency.

[McRuby]

I'm particularly concerned about fuel economy, so I've researched idling issues. For automatic transmissions, around 700 RPM is ideal. Reducing idle speed by 50 RPM can save 0.2 liters of fuel per 100 kilometers. However, don't casually lower the idle speed - below 600 RPM, engine vibration increases significantly and piston wear accelerates much faster. High idle speed is even worse; at 1000 RPM, the air-fuel ratio becomes unbalanced, causing nitrogen oxide emissions to surge dramatically. If waiting at a red light for more than two minutes, it's better to turn off the engine completely, especially for vehicles with start-stop systems. Older cars require regular throttle body cleaning, as carbon buildup can cause unstable idling and increased fuel consumption. Owners who've modified their cars with larger rims should note that increased tire resistance can cause a slight rise in idle speed.

[AaliyahRose]

From an engineering perspective, idle speed is the result of precise calculations by the ECU. Fuel-injected engines maintain 600-850 RPM when warmed up, as this range balances fuel consumption, emissions, and smoothness. The design accounts for the additional load from the AC compressor, automatically increasing RPM by about 100. New vehicles undergo idle calibration tests before leaving the factory, where parameters like coolant temperature, oil pressure, voltage, and intake pressure are input into the ECU to create a data map. During normal driving, a 2000-meter altitude change can cause idle speed to fluctuate by about 50 RPM, and high-altitude areas experience longer high-idle durations during startup. Abnormal RPM is usually 80% due to inaccurate sensor data, which an OBD scanner can pinpoint.