Idle Air Control System RPM Higher Than Expected
Idle RPM exceeds the target despite the IAC commanded fully closed. Almost always caused by a vacuum leak that lets air bypass the IAC — torn intake hose, leaking PCV, brake booster, or intake manifold gasket.
Affected components
- Intake manifold
- Pcv valve
- Brake booster
- Vacuum hose
Common causes
- High likelihood: Vacuum leak bypassing IAC
- Medium likelihood: PCV valve stuck open
- Medium likelihood: Brake booster diaphragm leaking
Possible symptoms
- Check engine light on
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.