Diagnostic Aids

Inspect for the following conditions:

• A skewed high Throttle Position (TP) sensor.
• Restricted air intake system.
• Objects blocking the IAC passage or throttle bore.
• The correct Positive Crankcase Ventilation (PCV) valve.
• A properly installed PCV valve.
• Proper operation of the PCV valve.
• Proper operation and installation of all air intake components.
• Proper installation and operation of the Mass Air Flow (MAF) sensor, if equipped.
• Evidence of damage or tampering of the following components:
  1. The throttle stop screw.
  2. The throttle plate.
  3. The throttle shaft.
  4. The throttle linkage.
  5. The cruise control linkage, if equipped.
• Excess deposits in the IAC passage or on the IAC pintle.
• Excess deposits in the throttle bore or on the throttle plate Vacuum leaks.
• Excess load on engine, such as energy-draining conditions of the transmission, power steering, or alternator.
• A high or unstable idle condition. This condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. See TROUBLE SHOOTING - NO CODES - TRUCKS article.
• A low or unstable idle condition. This condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. See TROUBLE SHOOTING - NO CODES - TRUCKS article.
• An intermittent condition.

Fig 1: Identifying IAC Valve Harness Connector Terminals

Courtesy of GENERAL MOTORS CORP.