P0505
Harley-Davidson Motorcycle
Severity:What Does This Error Mean?
Harley-Davidson P0505 means the idle air control (IAC) system has detected a fault — the engine idle speed is not being controlled correctly. A dirty throttle body, a failed IAC motor, or a vacuum leak are the most common causes.
Affected Models
- Harley-Davidson Touring
- Harley-Davidson Softail
- Harley-Davidson Dyna
- Harley-Davidson Street Glide
- Harley-Davidson Road King
Common Causes
- Dirty throttle body with carbon buildup preventing proper idle airflow
- Failed IAC (Idle Air Control) motor or stepper motor
- Vacuum leak in the intake system pulling unmetered air
- Throttle body gasket leak
- ECM or IAC wiring harness fault
How to Fix It
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Clean the throttle body.
Carbon buildup in the throttle bore is the most common cause of P0505 on older Harleys. Remove the air cleaner, spray throttle body cleaner into the bore, and work the throttle open and closed several times. Wipe clean.
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Check for vacuum leaks.
Inspect all intake hoses, the throttle body gasket, and intake manifold gaskets for cracks or loose connections. A vacuum leak lets unmetered air into the engine, making idle speed unpredictable.
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Test the IAC motor.
Use a Harley-Davidson compatible scan tool to command the IAC motor and confirm it responds. Alternatively, test the IAC motor windings with a multimeter — an open circuit confirms the motor has failed.
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Clear the code and verify idle.
After cleaning or replacing parts, clear P0505 and run the engine at operating temperature. Idle should stabilise at the correct RPM (typically 950–1,050 RPM for most Harley models). If idle hunts up and down, a vacuum leak still exists.
When to Call a Professional
If cleaning the throttle body and checking for vacuum leaks does not clear P0505, the IAC motor has likely failed. Harley dealers or independent technicians can test the IAC motor and replace it if necessary.