P0505
Idle Air Control System Malfunction
A general fault has been detected in the idle air control (IAC) system. On older vehicles with a separate IAC valve, this means the valve cannot maintain commanded idle RPM; on drive-by-wire systems, the equivalent fault is in the throttle body's idle adaptation.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Symptoms
- Check engine light on
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
Common causes
Ordered by how often each turns out to be the cause.
- IAC valve carboned, stickyCommon
- Throttle body dirty (drive-by-wire)Possible
- Vacuum leak affecting idlePossible
Parts involved
- Idle Air Control Valve
- Throttle Body
P0505 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.