All codes
P0505Engine Problems
Idle Air Control System Malfunction
Diagnose P0505 idle control code. Learn about the IAC valve and how to fix idle speed problems.
What you may notice
Symptoms
- 01Erratic idle speed
- 02Stalling at idle
- 03High idle speed
- 04Idle hanging after acceleration
- 05Check engine light on
Where to look first
Common causes
- 01Dirty IAC valve
- 02Failed IAC valve
- 03Vacuum leaks
- 04Throttle body carbon buildup
- 05Wiring/connector issues
Step by step
What to check and repair
- 01Clean IAC valve
- 02Clean throttle body
- 03Check for vacuum leaks
- 04Inspect wiring and connector
- 05Replace IAC valve if needed
What Does P0505 Mean?
P0505 indicates a malfunction in the Idle Air Control (IAC) system, which regulates engine idle speed by controlling airflow bypassing the throttle plate.
IAC Function
The IAC valve opens and closes to adjust idle speed based on engine load (AC, power steering, electrical loads, etc.).
Symptoms Pattern
Problems typically show up most during transitions - the idle may hang high after deceleration or drop too low and stall.