P0511 moderate

Idle Air Control Circuit

The P0511 code means the vehicle's onboard diagnostic system has detected: Idle Air Control Circuit. This is a moderate severity code.

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Keep driving?: Short distances only
DIY difficulty: moderate
Estimated cost: $50 - $300 (parts and labor)

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Common Symptoms

Check Engine Light on
Erratic or unstable idle speed
Engine stalling at idle
High idle speed

Probable Causes (Ranked by Likelihood)

Faulty idle air control (IAC) valve Very High
Carbon buildup in IAC valve or throttle body passages High
Wiring fault in IAC circuit Moderate
Vacuum leak affecting idle control Moderate

Step-by-Step Diagnostic Procedure

Use a scan tool to monitor IAC valve commanded position vs actual idle speed
Remove and inspect the IAC valve for carbon buildup; clean with throttle body cleaner
Check IAC valve wiring and connector for damage, corrosion, or loose connections
Test IAC valve by commanding it through its range using a scan tool and listening for movement

Frequently Asked Questions

What is the idle air control valve?

The IAC valve controls the amount of air bypassing the throttle plate at idle. By adjusting airflow, the ECM can maintain a stable idle speed under varying loads such as when the AC is turned on or the power steering pump is loaded.

Can cleaning the IAC valve fix P0511?

In many cases, yes. Carbon buildup is a common cause of IAC problems. Removing the valve and cleaning it with throttle body cleaner can restore proper operation. Also clean the passages in the throttle body.

Does my car have an IAC valve?

Many newer vehicles use electronic throttle control (drive-by-wire) instead of a separate IAC valve. These vehicles control idle speed directly through the throttle body motor. The IAC valve is common on older vehicles with cable-operated throttles.