P0505Idle Control System
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- CARB requires the idle speed control to be monitored: petrol engines must flag a fault if the target idle speed is not reached within +200/−100 rpm, diesels within ±30 %. Older engines use a separate idle air control valve that bypasses the closed throttle; with electronic throttle the throttle itself controls idle and no separate valve exists. P0505 is the general fault of the idle control, used where the maker does not separate too low from too high or the control is at its limit. With an idle valve it is typically sticking or gummed (Saab T5: idle outside 700–1200 rpm); on electronic throttles a Ford investigation shows P0505 from deposits in the throttle body. Ford's 2020–23 engines disable start-stop with P0505–P0507. Warning lamp behaviour depends on the maker.
- What you may notice
- Idle speed fluctuates, too high or too low
- Engine stalls at idle or when coasting
- Start-stop not working
- Likely causes
- LikelyThrottle body or idle valve dirty or gummed
- PossibleFalse air (hoses, intake gasket, crankcase ventilation)
- PossibleIdle valve faulty mechanically or electrically
- RareLearned values not reset after cleaning
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €40 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.