What Causes High Idle Speed in Cars During Winter?
2 Answers
The reason for high idle speed in cars during winter is: The normal operating water temperature of the engine is around 90 degrees. In extremely low temperatures, after the engine starts, the water temperature sensor sends a signal to the ECU, causing the engine to increase fuel injection and air intake, thereby raising the engine speed to quickly bring the engine to its normal operating temperature. As the engine temperature gradually rises, the idle speed will also gradually decrease to normal levels. The increase in idle speed after a cold start is a normal phenomenon, serving as a protective measure for the engine by the car, and also to improve combustion efficiency and meet emission standards. This phenomenon varies depending on the climate temperature. In northern regions, the increase in idle speed after starting the car is more significant and lasts longer, while in southern regions, this phenomenon is hardly noticeable.
I remember a few years ago when I drove my old car in Northeast China on mornings with temperatures below -20°C, the idle speed would always shoot up to over 1,000 RPM, making so much noise that the neighbors complained. I later asked a mechanic and learned that in extremely cold winter weather, the engine fluids become as thick as glue. The car's onboard computer automatically increases the idle speed to help quickly heat up the engine, allowing the coolant and oil to circulate and operate normally. This design is meant to protect the engine from wear and is a normal phenomenon. However, if the high idle persists for more than ten minutes or is accompanied by engine shaking, you should be cautious—it could be due to carbon buildup jamming the idle control valve or a faulty thermostat causing the temperature sensor to falsely report high values. After cleaning the throttle body myself once, the situation improved significantly, but it's still best to perform a comprehensive maintenance check before the cold weather hits. A high idle also consumes extra fuel; my monthly fuel consumption increased by about 10% every winter, but safety comes first.
