P0518moderate severityPowertrain
Idle Air Control Circuit Intermittent
on 2009 Audi A3 2.0L TDI · FWD
What this code means
The PCM has detected an intermittent fault in the idle air control (IAC) circuit. This can cause unstable idle behavior when the connection drops out momentarily.
Symptoms
- Erratic or fluctuating idle
- Occasional stalling
- Check engine light on
Common causes
- Loose or corroded IAC connector
- Damaged IAC wiring
- Faulty idle air control valve
- Poor PCM ground
Diagnostic steps
- Scan for stored and pending codes
- Inspect IAC connector and wiring for looseness
- Wiggle-test harness while monitoring live data
- Test IAC valve resistance and operation
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