Applicable Systems
OBD-II

Symptoms

IAC valve/actuator system fault; engine idle too high, too low, or stalling; ECM cannot control idle speed.

Possible Causes

  • IAC valve stuck open/closed
  • IAC valve carbon buildup
  • Throttle body coking
  • IAC wiring fault

Troubleshooting Steps

  1. Step 1: Check IAC valve operation with scanner (command idle up/down)
    RPM changes when IAC commanded
  2. Step 2: Inspect IAC valve for carbon buildup
    Valve clean
  3. Step 3: Clean throttle body and IAC valve
    No carbon buildup
  4. Step 4: Check IAC wiring
    Wiring intact
  5. Step 5: Replace IAC valve if no response
    Idle speed stable and correct

How to Reset

Clear with OBD-II scanner; may require idle relearn procedure.

Common Replacement Parts

  • IAC Valve (OEM spec)
  • Throttle Body Cleaner

Frequently Asked Questions

  • Q: What is IAC valve?

    Idle Air Control valve bypasses throttle plate to provide controlled air for idle. ECM adjusts IAC to maintain target idle RPM regardless of engine load (AC, alternator, etc.).

Related OBD-II Generic (SAE J2012) Fault Codes

Source: SAE J2012 standard DTC list + OBD-II portal

Category: OBD-II