The idle air control system regulates how much air bypasses the throttle plate at idle to keep engine speed steady. This general code means idle behavior is outside the expected range, without yet pinning down whether it's running too low or too high.
Symptoms
- Idle speed that hunts up and down instead of staying steady
- Engine occasionally stalls at stops, especially right after starting or when the AC kicks on
- Idle noticeably too high or too low compared to normal
- Rough or shaky idle
Likely causes
- Carbon buildup fouling the idle air control valve or throttle body — extremely common
- A vacuum leak affecting idle air balance
- Failed idle air control valve or electronic throttle body actuator
- Dirty or malfunctioning throttle position sensor feeding bad data to the idle control loop
How to diagnose it
- Inspect and clean the throttle body and idle air control valve — this alone resolves a large share of idle codes
- Check for vacuum leaks around the intake and throttle body gasket
- Test the idle air control valve's operation and the throttle position sensor's signal with a scan tool
Typical fixes & cost
- Clean the throttle body and idle air control valve60–150 EUR
- Replace the idle air control valve or throttle body actuator120–400 EUR
- Repair a vacuum leak60–250 EUR
Code names are compiled from open/standardized SAE and ISO references. Explanations, symptoms, causes and fixes are original. Covers generic (P0/C0/B0/U0) codes only — manufacturer-specific codes are planned for a future update.
AS
Reviewed by Artyom SemenovAutomotive Editor · Fact-checked by Yauheni Kapliarchuk, Editor-in-Chief