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Diagnostic Procedure

  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L ION article.
    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. Install scan tool. Start engine. Turn all accessories off. Using scan tool RPM control function, slowly increment engine speed to 1700 RPM, then to 600 RPM. Then to 1700 RPM. Exit RPM control function. Did the engine speed stabilize within 100 RPM less than the commanded engine speed or within 200 RPM above the Commanded RPM? If yes, see DIAGNOSTIC AIDS  . If no, go to next step.
  3. Turn ignition switch to OFF position. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J 37027-A), or equivalent, to the IAC valve. Start the engine. Command IAC valve in until about 600 RPM is reached and then command IAC valve out until about 1700 RPM is reached. Return engine RPM to desired idle as indicated on scan tool data list. Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the 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 during the last test? If yes, go to step  11 . If no, go to step  12 .
  5. Using a test light connected to ground, probe one IAC valve circuit at IAC valve harness connector. Start engine. Using IAC system motor analyzer, command high RPM while observing scan tool until IAC counts start to increment, then command low RPM until IAC counts start to increment. Observe test light while incrementing IAC counts. Return engine to idle as indicated on scan tool data list. Repeat procedure for other 3 IAC valve 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 IAC coil "A" low circuit and IAC coil "A" high circuit at IAC valve harness connector. Using IAC system motor driver, command low RPM while observing scan tool until IAC counts start to increment, then command high RPM until IAC counts start to increment. Observe test light while incrementing IAC counts. Return engine speed to desired idle as indicated on scan tool data list. Repeat procedure on IAC coil "B" low circuit and IAC coil "B" high circuit. Did the test light stay illuminated, never flashing, while the IAC counts where incrementing? If yes, go to next step. If no, go to step  17 .
  8. Check for poor connection at IAC valve harness connector. Did you find and correct the condition? If yes, go to step  18 . If no, go to step  13 .
  9. Turn ignition switch to OFF position. Disconnect ECM harness connectors. Using a DVOM, test the circuit where the test light remained off for the following:
    • An open circuit.
    • A short to ground.
    • A short to another IAC valve circuit.

    Did you find and correct the condition? If yes, go to step  18 . If no, go to step  13 .

  10. Turn ignition switch to RUN position. Using a DVOM, test the circuit where the test light remained illuminated for the following:
    • A short to voltage.
    • A short to another IAC valve circuit.

    Did you find and correct the condition? If yes, go to step  18 . If no, go to step  13 .

  11. Visually and physically inspect for the following:
    • Throttle body damage and tampering.
    • Skewed TP sensor signal.
    • Throttle lever screw tampering (if equipped).
    • Vacuum leaks.
    • Faulty, incorrectly installed PCV valve and hose (if equipped).
    • Throttle shaft binding.
    • Throttle linkage or cruise control linkage binding (if equipped).

    Remove IAC valve. Inspect for the following:

    • Clogged or debris in IAC passage.
    • Excessive deposits on throttle plate.
    • Excessive deposits in throttle bore.
    • 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. Visually and physically inspect for the following:
    • Throttle body damage and tampering.
    • Throttle lever screw tampering (if equipped).
    • Excessive deposits on throttle plate.
    • Restricted air intake system. A possible collapsed or clogged air intake duct, before and after the air filter element, a restricted air filter element or restriction at the throttle body intake screen, if equipped.
    • Remove IAC valve and inspect for excessive deposits on IAC valve pintle and in IAC valve passage.

    Repair as necessary. Did you find and correct the condition? If yes, go to step  18 . If no, go to step  15 .

  13. Check for intermittent and poor ECM harness connections. Did you find and correct the condition? If yes, go to step  18 . If no, go to next step.
  14. Disconnect the ECM harness connectors. Using a DVOM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step  18 . If no, go to step  17 .
  15. Check for poor IAC valve harness connection. Did you find and correct the condition? If yes, go to step  18 . If no, go to next step.
  16. Replace IAC valve. After repair, go to step  18 .
  17. Replace ECM. See ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - ION article. Program (flash) ECM with correct vehicle software and calibration. See ENGINE CONTROL MODULE REPROGRAMMING under PROGRAMMING in SELF-DIAGNOSTICS - 2.2L ION article. After repair, go to next step.
  18. Reconnect any disconnected components. Use the scan tool to clear any DTCs that may have set. Turn ignition switch to OFF position for 30 seconds. Operate the vehicle within conditions to verify the repair. Did you verify the repair? If yes, go to next step. If no, go to step  2 .
  19. With a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 2.2L ION article. If no, system is okay at this time.
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