Diagnostic Aids

Inspect for the following conditions:

• High resistance in an IAC valve control circuit.
• Proper operation and installation of all air intake components.
• Correct Positive Crankcase Ventilation (PCV) valve, properly installed and proper operation of PCV valve (if equipped).
• Proper installation and operation of the Mass Airflow (MAF) sensor, if equipped
• Tampered with or damaged throttle stop screw.
• Tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control linkage (if equipped).
• A skewed high Throttle Position (TP) sensor.
• Excessive deposits in IAC passage or on IAC pintle.
• Excessive deposits in throttle bore or on throttle plate.
• Vacuum leaks
• A high or unstable idle condition could be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Refer to SYMPTOMS under TROUBLE SHOOTING - NO CODES article.
• If the problem is determined to be intermittent, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article.