Idle Air Control Circuit Intermittent
The P0518 code indicates an intermittent fault in the idle air control (IAC) circuit. The IAC valve regulates engine idle speed by bypassing air around the throttle plate. An intermittent circuit issue can cause erratic idle, stalling, or poor performance. Common causes include a faulty IAC valve, damaged wiring, or a loose connector.
1. Most Common Causes
- Loose or corroded electrical connections at the IAC actuator or PCM
- IAC circuit wiring shorted, open, or with damaged insulation
- Intermittent internal failure of the idle air control solenoid/valve
- Intermittent fault in the PCM power relay or voltage supply
- False contacts caused by engine vibrations
2. Symptoms You Will Notice
- Intermittent rough idle or stalling
- Check Engine Light illuminated
- Idle speed fluctuating or too high/low
- Engine may stall when coming to a stop
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect IAC valve wiring and connector for damage or looseness.
Step 3: Test IAC valve resistance with a multimeter (specs vary by vehicle).
Step 4: Check for voltage and ground at the IAC connector with key on.
Step 5: If wiring is good, replace the IAC valve and clear codes.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It may be safe for short trips, but intermittent stalling can be dangerous. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on the vehicle and if the IAC valve needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.