Diagnostic Aids

Check for the following conditions:

• High resistance in an IAC valve control circuit.
• The correct Positive Crankcase Ventilation (PCV) valve, properly installed and proper operation of the PCV valve.
• Proper operation and installation of all air intake components.
• Proper installation and operation of the Mass Airflow (MAF) sensor, if equipped.
• A tampered with or damaged throttle stop screw.
• A 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 the IAC valve passage or on the IAC valve pintle.
• Excessive deposits in IAC valve passage or on IAC valve pintle.
• Excessive deposits in the throttle bore or on the 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.
• High or unstable idle condition caused by a non-IAC system problem that cannot be overcome by IAC valve.
• If the problem is determined to be intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.