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Home >> GMC >> 2003 >> Jimmy 2D Utility, Part Time, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing - 4.3L >> Idle Control System >> Idle Air Control System Diagnosis >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article. After performing Diagnostic System Check - Engine Controls, go to next step.
    2. NOTE: Ensure that the engine speed parameter stabilizes with each commanded RPM change to determine if the engine speed stays within 100 RPM less than the commanded RPM or within 200 RPM more than the commanded RPM.
  2. Set parking brake and block drive wheels. Start engine. Turn OFF all accessories. Using scan tool in RPM Control function, slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit the RPM Control function. Did the engine speed parameter stabilize within 100 RPM less than the commanded engine speed or within 200 RPM above the commanded RPM? If yes, go to DIAGNOSTIC AIDS . If no, go to next step.
  3. Turn ignition off. Disconnect the IAC valve. Connect an IAC Motor Driver (J-37027-1A) to the IAC valve. Start engine. Using IAC motor driver, command the IAC valve in until 600 RPM is reached. Command the IAC valve out until 1700 RPM is reached. Return engine speed to the desired idle speed parameter. Did engine speed parameter steadily decrease to 600 RPM and steadily increase to 1700 RPM when IAC valve was commanded in and out? If yes, go to step  5. If no, go to next step.
  4. Did you observe an excessively high idle condition that could not be controlled with the IAC motor driver? If yes, go to step  11. If no, go to step  12.
  5. Connect a test light between one of the IAC valve control circuits and a good ground. Start engine. Observe the IAC Counts parameter with scan tool. Using IAC Motor Driver (J-37027-1), command high RPM until the IAC Counts parameter starts to increment. Command low RPM until the IAC Counts parameter starts to increment. Return engine speed to the desired idle speed parameter. Repeat procedure for the other 3 IAC valve control circuits. Did the test light remain on, never flashing, while the IAC counts were incrementing for any of the IAC valve control circuits? If yes, go to step  10. If no, go to next step.
  6. Did the test light remain off, never flashing, while the IAC counts were incrementing for any of the IAC valve control circuits? If yes, go to step  9. If no, go to next step.
  7. Connect a test light between the IAC coil "A" low control circuit and IAC coil "A" high control circuit. See Fig 1. Observe the IAC Counts parameter with a scan tool and test light. Using IAC motor driver, command high RPM until the IAC counts parameter starts to increment. Command low RPM until the IAC counts parameter starts to increment. Return the engine speed parameter to the desired idle speed parameter. Repeat procedure with test light connected between the IAC coil "B" low control circuit and IAC coil "B" high control circuit. Did the test light stay illuminated, never flashing, while the IAC counts were incrementing? If yes, go to next step. If no, go to step  17.
  8. Test for an intermittent and for a poor connection at the IAC valve. Did you find and correct the condition? If yes, go to step  18. If no, go to step  13.
  9. Turn ignition off. Disconnect PCM. Test the circuit where the test light remained OFF for an open circuit, short to ground, or short to another IAC valve control circuit. Did you find and correct the condition? If yes, go to step  18. If no, go to step  13.
  10. Turn ignition on. Test the IAC valve control circuit where the test light remained illuminated for a short to voltage, or short to another IAC valve control circuit. Did you find and correct the condition? If yes, go to step  18. If no, go to step  13.
  11. Inspect throttle body for damage and tampering, a skewed TP sensor signal, throttle lever screw for tampering (if equipped) or vacuum leaks. Inspect for faulty or incorrectly installed PCV valve and hose, if equipped. Inspect throttle shaft for binding, throttle linkage or cruise control linkage for binding, if equipped. Remove IAC valve. Inspect for debris in IAC passage, excessive deposits on throttle plate, excessive deposits in throttle bore, or excessive deposits on IAC valve pintle. Did you find and correct the condition? If yes, go to step  18. If no, go to step  15.
  12. Inspect throttle body for damage and tampering, throttle lever screw for tampering (if equipped), excessive deposits on throttle plate, or restricted air intake system. Inspect for collapsed or clogged air intake duct, before and after the air filter element, a restricted air filter element, restriction at throttle body intake screen, if equipped. Remove IAC valve. Inspect for excessive deposits on the IAC valve pintle and in IAC valve passage. Did you find and correct the condition? If yes, go to step  18. If no, go to step  15.
  13. Test for an intermittent and for a poor connection at PCM. Did you find and correct the condition? If yes, go to step  18. If no, go to next step.
  14. Disconnect PCM. Test all IAC valve control circuits for high resistance. Did you find and correct the condition? If yes, go to step  18. If no, go to step  17.
  15. Test for an intermittent and for a poor connection at the IAC valve. Did you find and correct the condition? If yes, go to step  18. If no, go to next step.
  16. Replace IAC valve. After replacing IAC valve, go to step  18.
  17. Replace PCM. See REMOVAL & INSTALLATION - ASTRO & SAFARI or REMOVAL & INSTALLATION - BLAZER, JIMMY CANADIAN, SONOMA & S10 PICKUP article. Program replacement PCM. After repairs, go to next step.
  18. Reconnect any disconnected components. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Attempt to reproduce the original symptoms to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step  2.
  19. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L ASTRO, BLAZER, JIMMY CANADIAN, SAFARI, SONOMA & S10 PICKUP article. If no, system is okay.
Fig 1: Identifying Idle Air Control Valve Connector Terminals
G00101510Courtesy of GENERAL MOTORS CORP.
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