P0505: Idle Air Control System Malfunction
System: Idle, throttle, and boostThe computer cannot hold the engine at the idle speed it wants.
Severity: 2 of 4
Usually drivable, but stalling at stops or when the air conditioning kicks on is a real safety risk in traffic. If the engine stalls or races on its own, park it until it is fixed.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0505 means
At idle the throttle is almost closed, so the computer controls idle speed by letting a small, measured amount of air past it. Older engines use a separate idle air control (IAC) valve. Newer engines with electronic throttle control do the same job by opening the throttle plate slightly.
P0505 means idle speed is not following the computer's target, or the IAC circuit has an electrical fault. Carbon buildup in the IAC passage or throttle body is the classic cause.
After a battery disconnect or a throttle body cleaning, many vehicles need an idle relearn. Skipping it can cause unstable idle and this code.
Common causes (cheapest likely first)
- Carbon buildup in the IAC valve or throttle body. Cleaning with throttle body cleaner often helps.
- Vacuum leak. Extra air raises idle beyond what the computer can control.
- Failed IAC valve. Replace if cleaning does not help or the circuit tests bad.
- Idle relearn not done. Needed on many vehicles after battery or throttle work.
- Wiring or connector fault. Check for corrosion and loose pins.
Symptoms
- Idle too high or too low
- Idle hunting up and down
- Stalling when coming to a stop
- Stalling when the air conditioning turns on
- Check engine light
DIY difficulty: Easy to moderate
Cleaning the throttle body and IAC valve is a common DIY job. On electronic throttle bodies, do not force the plate open by hand; follow the service manual and run the idle relearn afterward.
Tools: OBD-II scanner, Throttle body cleaner, Screwdrivers or Torx bits, New IAC gasket, Smoke tester (optional)
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Throttle body and IAC cleaning | $5 to $15 | 0.3 to 1.0 h | $5 + 0.3 × $110 = $38 $15 + 1.0 × $190 = $205 |
| IAC valve | $40 to $250 | 0.3 to 1.5 h | $40 + 0.3 × $110 = $73 $250 + 1.5 × $190 = $535 |
| Vacuum hose | $10 to $80 | 0.3 to 1.0 h | $10 + 0.3 × $110 = $43 $80 + 1.0 × $190 = $270 |
Watch a repair video
Search YouTube for “P0505 fix” videos. Pick a recent video that matches your engine, and confirm the diagnosis before buying parts.
By make
This code works the same way on every make. See brand notes.
Repair manuals
Step-by-step service manuals with torque specs and wiring diagrams:
Haynes manuals Chilton manuals
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Related codes
Check for recalls
Before paying for a repair, enter your VIN in the NHTSA recall lookup. Emissions parts may also be covered by a federal emissions warranty; check your warranty booklet.
FAQ
Can a dirty throttle body cause P0505?
Yes. Carbon changes how much air slips past the throttle at idle, and the computer can run out of adjustment.
Why did P0505 appear after I changed my battery?
The computer may have lost its learned idle settings. Many vehicles have an idle relearn procedure; check the owner or service manual.
Is P0505 dangerous?
The code itself is not, but stalling in traffic can be. Fix it soon if the engine stalls.