P0506
Idle Air Control System RPM Lower Than Expected
The engine idles below the target RPM despite the IAC opening fully. Indicates restricted air path past the IAC — typically a heavily fouled throttle body or stuck IAC valve.
- 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.
- Throttle body or idle bypass passage cloggedCommon
- IAC valve stuck mostly closedPossible
Parts involved
- Idle Air Control Valve
- Throttle Body
P0506 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.