IAC Valve Problems

An IAC valve adjusts the engine's idle speed, but can develop problems.

An idle air control (IAC) motor adjusts the engine's idle speed, or RPM, by opening or closing an air bypass valve located in the throttle body. IAC valve problems can develop for many reasons, but can usually be resolved through a little detective work.

Short Circuit

An IAC motor can short circuit due to bad wiring or an overload of current, causing the motor to operate the valve more slowly or not at all, which in turn can result in the engine stalling at idle. Replacing the failed motor unit typically restores correct IAC valve function.

Carbon Buildup

Over time, carbon can accumulate in the IAC motor, leading to poor control of the IAC valve and subsequent poor engine idling and stalling problems. Removing carbon or other sediment from the motor with cleaner typically corrects the IAC valve problem.

Bad Hose

A vacuum hose connects the IAC motor to the intake manifold in some vehicle models. A torn hose causes the engine to lose vacuum, affecting how the IAC motor opens and closes the IAC valve.

References

• AutoMedia: Sensor Troubleshooting: Idle Air Control Valve
• "How to Repair Your Car"; Paul Brand; 2006

Resources

• "The Complete Idiot's Guide to Auto Repair"; Vyvyan Lynn and Tony Molla; 2007