System Symptom Troubleshooting Guides

1. When the idle speed is out of specification and the Malfunction Indicator Lamp (MIL) does not blink Diagnostic Trouble Code (DTC) 14, check the following items:
Adjust the idle speed
Air conditioning signal
Alternator FR signal
A/T gear position signal
Starter switch signal
Brake switch signal
PSP switch signal
Fast idle thermo valve
Starting Air Valve
Hoses and connections
Idle Air Control (IAC) Valve and its mounting 0-rings

2. If the above items are normal, substitute a known-good IAC Valve and readjust the idle speed, refer to Adjustments/Idle Speed.

If the idle speed still cannot be adjusted to specification (and the MIL does not blink code 14) after IAC Valve replacement, substitute a known-good Engine Control Module (ECM) and recheck. If symptom goes away, replace the original ECM.