P0505
Idle Air Control System Malfunction
medium
i Description
The Idle Air Control (IAC) system is not functioning correctly. The IAC valve controls the amount of air bypassing the throttle plate to maintain the target idle speed. On electronic throttle vehicles, this code indicates the ECU cannot achieve the target idle.
? Common Causes
- Carbon-clogged IAC valve
- Faulty IAC valve motor
- Vacuum leak affecting idle control
- Dirty throttle body
- Wiring fault to IAC valve
! Symptoms
- Erratic idle speed
- Engine stalling at idle
- Idle too high or too low
- Hunting idle (RPM bouncing up and down)
# Diagnostic Steps
- Remove and clean IAC valve with throttle body cleaner
- Clean the throttle body
- Check for vacuum leaks
- Test IAC valve motor operation
- Monitor idle RPM and IAC duty cycle with scan tool
⚙ Typical Fix
Clean or replace the IAC valve. Clean the throttle body.
Parts Needed
IAC valve, Throttle body cleaner, Gaskets
Estimated Cost
$50-$300
↔ Related Codes
Q Frequently Asked Questions
Yes, but the idle may be very rough and the engine might stall at stops. Be prepared to keep your foot on the gas at traffic lights.
Yes. Cleaning the IAC valve and throttle body is a great DIY project. Often this alone fixes the issue.
☞ Learn More
- What is OBD-II? — Complete guide to your car's diagnostic system
- How to Read DTC Codes — Step-by-step with a Bluetooth scanner
- OBD-II Scanner Buying Guide — Find the best scanner for your car