The idle speed stays below the target. The driver may notice rough idle, vibration or stalling.
Likely causes, most common first
- Dirty throttle body
- Blocked idle air path
- Engine load from a seized accessory
- Low engine compression
Parts usually involved
- Throttle body
- Idle air control valve
Test before you replace
Clean and inspect the throttle body and compare idle speed with the target on a scan tool.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.