EngineLightCodes
Powertrain code

P0505 Idle Control System

Severity
Fix soon
Typical repair cost
$40–$660
Do it yourself
Possible, medium
Shop time
0.5–2 hours

CARB requires the idle speed control to be monitored: gasoline engines must flag a fault if the target idle speed is not reached within +200/−100 rpm, diesels within ±30 %.

How the engine computer detects it

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 behavior depends on the maker.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Idle speed fluctuates, too high or too low
  • Engine stalls at idle or when coasting
  • Start-stop not working

Common causes

  1. Throttle body or idle valve dirty or gummed Most likely
  2. False air (hoses, intake gasket, crankcase ventilation) Possible
  3. Idle valve faulty mechanically or electrically Possible
  4. Learned values not reset after cleaning Less likely

How to diagnose P0505

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: idle control, throttle body, idle air control valve, engine control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
5
Vehicle speed, idle control and auxiliary inputs
05
Specific fault

Questions drivers ask

Can I drive with code P0505?

Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.

Will my car pass an emissions inspection with P0505?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0505 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0505 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0505. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.