What Does P0518 Mean?
The idle air control (IAC) circuit is experiencing intermittent electrical faults. The PCM has detected the IAC motor circuit signal dropping out or fluctuating intermittently, which means the idle control system is losing the ability to regulate idle speed at random intervals. The driver may notice the idle speed hunting (surging up and down), occasional stalling, or the idle speed changing unpredictably.
Common Causes
30%
Intermittent connection at the IAC valve connector due to worn terminals
25%
Chafed or damaged IAC wiring with intermittent contact
25%
Failing IAC motor with intermittent internal winding breaks
12%
IAC valve binding intermittently due to carbon buildup
8%
Loose PCM connector pin for the IAC circuit
Diagnostic Steps
1
Monitor IAC step count or duty cycle while wiggling the IAC connector and harness — look for sudden changes that indicate an intermittent connection.
2
Remove and inspect the IAC valve pintle for carbon deposits or binding. Clean with throttle body cleaner and verify smooth movement throughout the full range.
3
Check IAC motor winding resistance while flexing the wiring — resistance should remain stable. Any fluctuation indicates an intermittent break in the winding or wiring.
4
Inspect the IAC connector terminal tension by gently pulling on each wire — terminals should be firmly seated. Push on each terminal to verify spring tension is adequate.
5
Check the PCM connector for the IAC circuit pins — verify they are not backed out or have loose tension. Reseat the PCM connector and ensure the latch is fully engaged.
Estimated Repair Cost
$50 - $300
Parts + labor, varies by vehicle and location
The idle air control (IAC) circuit is experiencing intermittent electrical faults. The PCM has detected the IAC motor circuit signal dropping out or fluctuating intermittently, which means the idle control system is losing the ability to regulate idle speed at random intervals. The driver may notice...
The most common cause of P0518 (Idle Air Control Circuit Intermittent) is: Intermittent connection at the IAC valve connector due to worn terminals
Typical repair costs for P0518 range from $50 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The engine may stall intermittently and without warning, which is dangerous in traffic or at intersections. Idle speed may surge unpredictably, causing the vehicle to lurch. Drive with extra caution and avoid situations where a sudden stall would be hazardous.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0518 to identify the root cause.
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Quick Info
Category
Powertrain
System
Idle Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
