What Causes High Idle Speed During Cold Start?
2 Answers
The reason for high idle speed during cold start is that the combustion chamber temperature in the cylinders is low, leading to poor gasoline atomization. To meet the necessary combustion conditions, the engine ECU increases fuel injection, resulting in higher RPM. This is a normal phenomenon. After the engine warms up, the RPM will gradually decrease to around 800-1000. The main causes of engine shaking during cold start include: 1. Excessive carbon deposits on the throttle body, fuel injectors, or intake passages; 2. Mechanical failures in ignition coils, spark plugs, or fuel injectors; 3. Low oil pressure or cylinder pressure; 4. Poor fuel quality; 5. Damaged or dirty idle control valve. Solutions: 1. Check and clean carbon deposits on spark plugs; 2. Inspect the coolant temperature sensor and replace if necessary.
I've been driving for over 20 years, and every time I start the engine in cold weather, the RPM is always a bit higher, especially when starting up in winter mornings—the tachometer jumps to around 1500 RPM. This is completely normal: the car's computer system detects the low engine temperature and injects extra fuel and air to increase the RPM, helping the engine warm up faster and reducing cold wear. Additionally, cold engine oil is thicker, like heavy sauce, increasing friction resistance, which also raises the idle speed. After about a minute, as the temperature rises and the oil thins out, the RPM naturally drops to 700-800. If the idle speed doesn’t come down after two minutes or fluctuates with unusual noises, there might be a fault—like a broken temperature sensor or a clogged intake system—so it’s best to get it checked at a garage to avoid higher fuel consumption or part damage. Choosing the right engine oil, such as 5W-30, can help mitigate this effect. Remember, it’s the engine’s natural protective response, so don’t worry too much about it.
