P0507Idle air control RPM higher than expected

Means the ECM cannot bring idle down to the target: commanded idle air control still leaves rpm above the expected window. Drivers feel a high idle at stop, a surge when shifting to Park/Neutral, and a check-engine light that may set after several warm idle episodes. Freeze frame usually shows warm coolant, closed throttle, and rpm stuck hundreds above target.

Shop frequency: vacuum leak or unmetered air after the throttle (cracked hose, brake booster, PCV), then a dirty throttle body that will not seat closed, then a sticking IAC/idle stepper or electronic throttle plate. Next: incorrect idle relearn after battery/throttle service, leaking purge valve adding fuel vapor at idle, or rare ECM idle strategy faults. Do not start with a new throttle actuator if a hissing booster hose is the real path—prove where the extra air enters.

Diagnosis: graph desired vs actual idle rpm and throttle angle at hot curb idle. Spray or smoke for vacuum leaks with the engine hot. Clean the throttle bore and plate per OEM (do not jam rags into electronic throttles). Command IAC/ETB idle airflow and watch response. Check purge command at idle—if purge stuck open, rpm and fuel trim climb together. Perform the OEM idle relearn after repairs. Replace IAC or throttle body only when leaks are sealed and relearn still cannot hold target. Dig elsewhere when AC load or power-steering input never raises load compensation correctly, when a large intake gasket leak only appears hot, or when P0171 rides with the high idle. System context: high idle is excess air the controller cannot cancel—fix plumbing and throttle seating before programming myths.