OBD-II Code · Fuel & Air
P0505
Idle Air Control System Malfunction
Severity
medium
Worth booking. It costs fuel, emissions or comfort until it is fixed.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$80–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
The IAC valve isn't controlling idle speed.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Stalling at stops
- High or low idle
- Check engine light
Likely causes
- Carbon in IAC passageMost common
- Failed IAC valve
- Vacuum leak
Read the full diagnostic procedureP0505 is the generic Idle Air Control system fault and applies only to cable-throttle vehicles, not drive-by-wire (ETC) cars.
P0505 is the generic Idle Air Control system fault and applies only to cable-throttle vehicles, not drive-by-wire (ETC) cars. The PCM commands the IAC valve, a stepper motor or pintle that meters air around a closed throttle plate, and watches actual RPM versus target. If commanded position and resulting RPM disagree by more than the allowable window, P0505 sets.
Cheapest-first diagnosis
- scan IAC step count or duty cycle at warm idle in park with all accessories off, a healthy IAC typically sits between 15 and 40 steps (GM) or 25 to 45 percent duty (Ford).
- If the count is pegged at 0 or at the max (commonly 180 to 255 steps), the PCM has run out of authority, which means either a vacuum leak (high steps) or a stuck-open IAC/leaking gasket (low steps).
- Smoke-test the intake for leaks before touching the IAC, this finds the fault in roughly half of P0505 cases.
- Remove the IAC and clean the pintle and seat with throttle body cleaner, then perform an idle relearn (key on 5 minutes, key off 30 seconds, restart and idle 3 minutes with no load).
- The expensive misdiagnosis is buying a new IAC and a new throttle body when a $15 PCV valve and a smoke test would have solved it.
Vehicle-specific patterns1996 to 2005 GM 4.3L/4.8L/5.3L/6.0L trucks set P0505 from a clogged IAC pintle, GM TSB 03-06-04-030 covers the cleaning procedure.
- 1996to 2005 GM 4.3L/4.8L/5.3L/6.0L trucks set P0505 from a clogged IAC pintle, GM TSB 03-06-04-030 covers the cleaning procedure.
- 1996to 2000 Honda Civic and CR-V set P0505 from a failing IAC valve solenoid winding, Honda part 16022-P2A-J01.
- 1998to 2003 Ford Ranger and Explorer with 4.0L SOHC set P0505 from carbon at the IAC bore, plus a leaking lower intake gasket.
- 2000to 2004 Jeep Wrangler TJ with 4.0L sets P0505 from an aged IAC stepper motor.
Estimated repair$25 to $280.
Look up another code
P0505 — frequently asked
What does a P0505 code mean?
The IAC valve isn't controlling idle speed.
What causes a P0505 code?
Common causes: Carbon in IAC passage; Failed IAC valve; Vacuum leak.
What are the symptoms of a P0505 code?
Typical symptoms: Stalling at stops; High or low idle; Check engine light.
Is it safe to drive with a P0505 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $80-$400.
How do I diagnose a P0505 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
More free tools