P0518Idle Air Control Circuit Intermittent
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Older engines without electronic throttle have a separate idle air control valve bypassing the closed throttle; CARB requires its output to be checked but not the fault types to be coded separately. P0518 means its circuit fails sporadically – the signal or current briefly leaves its valid range and returns. No manufacturer document available to us uses P0518; GM and Ford report idle valve faults as P0505–P0507 and P0511. Engines with electronic throttle do not set it.
- What you may notice
- Fluctuating idle
- Engine stalls when coasting or stopping
- Check engine light (depending on the maker)
- Likely causes
- LikelyLoose contact or corrosion at the idle valve connector
- PossibleBroken or chafed wire in the harness
- PossibleValve coil with shorted turns (temperature-dependent)
- RareDriver in the engine module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €0 – €200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.