P0506: Idle Air Control System RPM Lower Than Expected
What to do
Expect a low, lumpy idle and possibly stalling at junctions. Note whether it is worse with the air conditioning or headlights on — that points at load rather than airflow.
What this code means
Idle speed is below target despite the module asking for more air. The control has run out of authority in the opening direction, which narrows the cause considerably: something is restricting airflow, or adding load the module cannot see.
Carbon around the throttle plate is the usual mechanism, and here cleaning genuinely is the repair rather than a delay tactic — deposits physically reduce the bypass area. Excessive electrical or mechanical load also produces this, so an air conditioning compressor that is dragging or an alternator working hard on a failing battery both belong on the list.
Likely causes
Start here
Less common
- Restricted air filter · easy
- Excessive engine load from accessories · moderate
- Faulty idle air control valve · moderate
- Binding throttle plate or linkage · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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