P0518 Idle Air Control Circuit Intermittent

P0518 indicates an intermittent idle air control circuit. The idle control signal or actuator feedback drops out, spikes, or becomes unstable part of the time.

Code details

Generic OBD-II · P0

System: Speed / Idle
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not call P0518 repaired after a steady idle test if the fault only appears during load transitions.

Symptoms of P0518

Unstable, high, or low idle, or stalling.
Erratic speedometer, cruise-control, or shift behaviour.
Check-engine light with a hesitation or surge.

Common causes of P0518

A dirty throttle body, idle-control valve, or throttle-position sensor.
A failing vehicle-speed or wheel-speed sensor, or its wiring.
Vacuum leaks or a related sensor forcing the idle/speed strategy.

Useful checks before replacing parts

Review idle speed history, IAC command, control voltage, throttle position, fuel trims, freeze-frame data, and whether the issue appears hot, cold, or during load changes.
Inspect connector tension, harness flex points, actuator movement, carbon buildup, vacuum leaks, grounds, and wiring near heat or vibration sources.
Graph idle command and RPM while moving the harness and changing loads such as A/C, steering, or gear engagement.

Related OBD-II codes

These nearby speed / idle entries can help compare wording and pin down the fault area.