Applicable Systems
OBD-II
Symptoms
Engine idle RPM below target; IAC valve or electronic throttle not providing enough air at idle; engine may stall.
Possible Causes
- IAC valve stuck closed or carbon buildup
- Throttle body coking
- Vacuum leak causing unmetered air (IAC closes to compensate, RPM drops)
Troubleshooting Steps
- Step 1: Check IAC valve operation with scanner
IAC responds to commands - Step 2: Inspect throttle body for carbon buildup
Throttle body clean - Step 3: Check for vacuum leaks
No leaks - Step 4: Clean IAC valve and throttle body
Components clean - Step 5: Clear code and perform idle relearn
Idle RPM at target
How to Reset
Clear with OBD-II scanner; requires idle relearn procedure.
Common Replacement Parts
- IAC Valve (OEM spec)
- Throttle Body Cleaner
Frequently Asked Questions
- Q: What is idle relearn?
Procedure where ECM learns correct idle IAC position. May require: key ON 1 min, key OFF 1 min, start and idle 10 min. Some vehicles need scanner-driven relearn.
Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II