PaulAllen on Nostr: Definitely not due to cold weather. Seems to be more common in small and/or Asian ...

Definitely not due to cold weather. Seems to be more common in small and/or Asian vehicles.

In our case "high" is 1500-2000 rpm and "longer period" is at least ten minutes or until about a minute into driving.

From ppq.ai:

There are several reasons why car engines may idle at a high RPM for a longer period during a cold start, particularly in the morning:

1. **Cold Weather**: In cold conditions, the engine needs to reach its optimal operating temperature. Higher RPMs help speed up this warming process.

2. **Engine Warm-Up**: Modern engines, especially those with fuel injection systems, are designed to run at a higher idle speed initially to facilitate faster warming and ensure oil circulates effectively.

3. **Emissions Control**: Higher RPMs help the catalytic converter reach the temperature needed to effectively reduce emissions.

4. **Battery Charging**: After a cold start, the alternator works harder to recharge the battery from the initial draw required to start the engine. Higher RPMs aid this process.

5. **Idle Air Control Valve**: The Idle Air Control (IAC) valve adjusts the amount of air entering the engine to stabilize the idle speed. It might cause higher RPMs until the engine is warm enough to maintain a consistent idle.

6. **Sensor Functionality**: Various sensors (like the coolant temperature sensor) provide data to the engine control unit (ECU), which adjusts the idle speed based on the data received to ensure proper operation.

If the high idle persists beyond the usual warm-up time or seems excessively high, it could be an indication of:

- A stuck or malfunctioning Idle Air Control (IAC) valve.
- A vacuum leak in the intake system.
- Faulty sensors (like the coolant temperature sensor or throttle position sensor).
- Issues with the ECU or its programming.

For persistent or unusual idling behavior, it’s advisable to consult a mechanic for a thorough inspection and diagnosis.