What is the suitable idling speed for an automatic transmission car?
4 Answers
Automatic transmission cars have a suitable idling speed between 800 and 1000 RPM. The gears of an automatic transmission car are as follows: N gear is neutral, P gear is parking, R gear is reverse, and L gear is low speed. Precautions for shifting gears in an automatic transmission car: 1. Do not press the accelerator pedal when shifting gears; 2. Do not immediately press the accelerator pedal hard after engaging a gear; 3. The vehicle can only be started in P or N gear; 4. The gear lever must be removed from P gear by stepping on the brake; 5. Do not shift into N gear to coast while driving; 6. Do not push into P gear while the car is moving; 7. When changing the direction of travel, switching between D and R gears must be done after the vehicle has come to a complete stop; 8. Placing the gear in N while driving prevents the oil pump from supplying oil normally for lubrication, which can cause the temperature of internal transmission components to rise and lead to damage.
Having driven automatic transmission cars for over a decade, I've noticed that during cold starts, the RPM might surge to around 1000, but after a few minutes of driving when the engine warms up, it stabilizes at approximately 700 RPM. If the needle consistently dips below 500 RPM when idling at a red light, the car tends to shake violently as if struggling for breath—that's when you should check for carbon buildup in the throttle body. Conversely, if it frequently climbs above 900 RPM, fuel consumption will undoubtedly be high, especially noticeable when running the AC in summer. My advice is to get an OBD scanner and connect it to your phone to monitor real-time data after the engine is fully warmed up. As long as the RPM stays steady around 700 with smooth operation and no shaking, there's generally no issue. Also, don't overlook the impact of oil viscosity—5W30 and 0W20 oils can affect idle stability differently.
Over the years of repairing cars, I've seen too many engines scrapped prematurely due to idle speed issues. The ideal idle speed for automatic transmissions typically ranges between 650-750 RPM, where the oil pump can just maintain stable oil supply to protect components. If it consistently runs below 600 RPM, the crankshaft can't properly drive the AC compressor and water pump, leading to inevitable engine overheating. Exceeding 850 RPM is even worse – piston ring wear can accelerate threefold. Last week, a Camry was towed in for unstable idle, and we ultimately found its fuel injectors clogged from long-term use of substandard gas from small fuel stations. I recommend regular fuel system cleaning and monthly monitoring of cold/hot idle speed variations – don't wait for the check engine light to act.
During the driving test, the instructor repeatedly emphasized: the standard idle speed for an automatic transmission after warming up is around 700 RPM. This RPM allows the car to maintain traction the moment the brake is released on a slope, preventing rollback. Once, while queuing in an underground mall parking lot, the car in front suddenly braked hard. Thanks to my car's stable idle speed of 750 RPM, when I released the brake for half a second, the car moved smoothly and avoided a rear-end collision. In contrast, my friend's car, which always shakes at 550 RPM, jerks forward every time it starts, as if being kicked in the rear. Remember, idle speed isn't just about parameters—it directly relates to driving safety, especially when maintaining a safe distance in rainy or foggy conditions while also keeping an eye on the tachometer.
