P0511

What it means

P0511 is the generic code for a fault in the idle air control (IAC) circuit. The engine control unit commands the idle air control device to hold the target idle speed, and it has detected an electrical problem in that circuit or a mismatch between the commanded and actual response. The exact test it uses and the type of device (stepper motor, rotary valve or throttle-body motor) depend on the vehicle and engine.

Symptoms

• Rough, hunting or surging idle
• Idle speed too high or too low
• Engine stalls when coming to a stop or when the air conditioning or lights switch on
• Difficult starting or stalling just after starting
• Malfunction indicator lamp on

Possible causes

• Idle air control valve sticking or clogged with carbon depositslikely
• Faulty idle air control valve or motor (internal open or short circuit)likely
• Damaged wiring, corroded or loose connector in the IAC circuit (open circuit, short to earth or short to supply)likely
• Unmetered air leak such as a split intake hose or vacuum leak upsetting idle controlpossible
• Dirty throttle body or restricted idle air passagespossible
• Fault in the engine control unit driver circuitrare

How to diagnose

1. Read the stored codes and freeze frame data to see engine speed, temperature and load when the fault set, and check for other codes, especially air flow, throttle or lean codes.
2. Inspect the IAC device connector and wiring for chafing, corrosion, bent pins, oil contamination and loose fit.
3. Check the intake system for split hoses, loose clamps, and vacuum leaks, and listen for hissing at idle.
4. Watch live data for idle speed against target and the IAC command, and see whether the device responds when idle demand changes.
5. Check the device resistance and supply, earth and control signals against the manufacturer's specification for that model.
6. Remove and inspect the idle air control device or throttle body for carbon build-up and free movement, where the design allows.
7. Command the device with a suitable bi-directional test if supported and see whether idle speed changes smoothly.
8. If the circuit tests good and the device is serviceable, check the control unit output and for any applicable software updates for that model.

How to fix

• Clean the idle air control valve and throttle body passages using a method suitable for that design, then clear the code and check idle.
• Replace the idle air control valve or throttle body assembly if it is faulty or will not move freely.
• Repair or replace damaged wiring and connectors, and clean the terminals.
• Repair vacuum leaks and replace split or loose intake hoses and seals.
• Carry out any idle or throttle relearn procedure that the manufacturer requires after cleaning or replacement.

Can I keep driving?

Nearby codes

• P0510GenericClosed Throttle Position Switch
• P0512GenericStarter Request Circuit