P0505moderate severityPowertrain
Idle Air Control System
on 2004 Subaru Legacy 3.0L H6 · AWD
What this code means
Malfunction in the idle air control (IAC) system.
Symptoms
- Erratic idle speed
- High idle
- Low idle
- Stalling at idle
- Fluctuating RPM
Common causes
- Faulty IAC valve
- Carbon buildup in IAC or throttle body
- Vacuum leak
- PCM issue
Diagnostic steps
- Clean IAC valve and passages
- Clean throttle body
- Test IAC valve operation
- Check for vacuum leaks
- Monitor idle RPM with scan tool
Repair notes
Clean IAC valve and throttle body first. Replace IAC if cleaning fails.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1