OBD-II code guide
P0505 Idle Control System Malfunction
P0505 means the engine computer cannot control idle speed as expected.
What it means
Idle speed may be too high, too low, unstable, or not responding to control commands.
Common symptoms
- High idle
- Low idle
- Stalling
- Surging idle
- Check engine light
Likely causes
- Dirty throttle body
- Vacuum leak
- Idle air control fault
- Wiring issue
- Throttle relearn needed
First checks
- Inspect intake hoses and vacuum lines.
- Check throttle body cleanliness.
- Review recent battery disconnect or throttle service.
- Scan desired versus actual idle speed.