What P0505 Means
The engine control module can't keep the idle speed within its expected range, either too high, too low, or fluctuating.
Common Causes
- Dirty or carbon-fouled throttle body/idle air control valve
- Vacuum leak
- Failing idle air control (IAC) valve
- Carbon buildup on intake valves
Symptoms You Might Notice
- Idle that hunts up and down or is unusually high/low
- Stalling at stops in severe cases
- Check engine light on
What to Check First
- 1
Clean the throttle body and idle air control valve — this resolves the majority of cases
- 2
Check for vacuum leaks around the intake
- 3
Test the IAC valve's operation and replace if faulty