Why does the idle speed stay high immediately after starting a cold engine?

[DiEmerson]

The reasons for high idle speed when starting a cold engine: 1. The engine requires greater torque to transition from stationary to operational state. Therefore, during initial startup, the ECU controls increased air intake and fuel injection to ensure smooth engine ignition and operation. 2. During cold starts, lower temperatures result in suboptimal ignition conditions and poor fuel atomization in the cylinders, leading to incomplete combustion of the air-fuel mixture. 3. Since the engine hasn't reached optimal operating temperature, increased friction occurs between pistons and cylinder walls, as well as among moving components. This unstable operating condition necessitates higher RPM to prevent stalling after startup. 4. To rapidly achieve normal operating temperature (reducing wear on friction components) and quickly heat the catalytic converter to its optimal conversion range (minimizing emissions), the engine maintains elevated RPM to accelerate coolant temperature rise - this constitutes the warm-up process.

[Lance]

I've been driving for decades, and it's perfectly normal for the idle speed to be high when starting a cold engine. This is the engine warming itself up in low temperatures. The coolant temperature sensor detects the cold state, and the ECU increases the fuel injection to raise the RPM a bit, helping the engine warm up quickly to reduce wear. Especially in winter when the engine oil is more viscous, a higher idle speed helps lubricate the engine components better. After driving for a couple of minutes, once the temperature gauge starts moving, the RPM will drop—no need to worry. However, if it doesn’t drop or fluctuates significantly, it might be due to carbon buildup clogging the throttle body or a faulty sensor. If this persists, it can increase fuel consumption and damage the engine. It’s recommended to check the air filter and cooling system every six months to keep them clean, ensuring smoother starts. In short, don’t let small issues escalate—address them early to save both hassle and money.