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. This may be due to a loose connection, damaged wiring, or a failing IAC valve.
01. Most Common Causes
- Faulty idle air control valve
- Damaged or corroded wiring/connectors in the IAC circuit
- Intermittent open or short in the IAC circuit
- Engine control module (ECM) issues
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Erratic idle speed (too high or too low)
- Engine stalling, especially when coming to a stop
- Poor acceleration or hesitation
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data to confirm P0518 and check for related codes.
Step 2: Visually inspect the IAC valve wiring and connector for damage, corrosion, or loose pins.
Step 3: Test the IAC valve resistance and operation using a multimeter and scan tool (if applicable).
Step 4: Check for intermittent faults by wiggling the wiring harness while monitoring IAC circuit voltage or scan tool data.
04. Commonly Affected Makes
05. 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 whether the IAC valve needs replacement or just a wiring repair.