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Idle Control System

NOTE: For idle control system testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.

  1. Idle Air Control (IAC) System Diagnosis (3.1L, 3.4L, 3.5L & 3.8L)

    If On-Board Diagnostic (OBD) system check has been performed, go to next step. If On-Board Diagnostic (OBD) system check has not been performed, perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article.
  2. Install scan tool. Start engine. Turn all accessories off. Using scan tool, command idle up to 1500 RPM, then down to 650 RPM and then back up to 1500 RPM. If engine speed responded as commanded within 50 RPM, system is okay. If engine speed did not respond as commanded within 50 RPM, go to next step.
  3. Turn ignition off. Connect IAC Driver (J-37027-A) to IAC valve. Set parking brake and block wheels. Start engine and let idle. Using scan tool, command idle up to 1500 RPM, then down to 650 RPM and then back up to 1500 RPM, while observing noid lights on IAC driver. If noid lights do not cycle Red and Green or turn off, go to next step. If noid lights cycle Red and Green but never off, go to step  5.
  4. Check for open, short to voltage or short to ground in IAC circuits between IAC valve and PCM. If problem does not exist, go to step  10. If problem exists, repair as necessary and go to step  12.
  5. If low idle or rich condition exists, go to next step. If low idle or rich condition does not exist, go to step  7.
  6. Check for the following conditions: throttle body damage, restricted intake system or air filter element, collapsed air intake duct, clogged IAC passages in throttle body, and intake leaks. If problem does not exist, go to step  8. If problem exists, repair as necessary and go to step  12.
  7. Check for the following conditions: vacuum leaks, damaged throttle body, throttle linkage binding, misadjusted throttle cable, misadjusted cruise control cable, and faulty PCV system. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step  12.
  8. Check for poor connection at IAC valve. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step  12.
  9. Replace IAC valve. After repairs, go to step  12.
  10. Check for poor connection at PCM. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step  12.
  11. Replace PCM. After repairs, go to next step.
  12. Clear all DTCs. Start engine. Ensure all accessories are off. Using scan tool, command idle up to 1500 RPM, then down to 650 RPM and then back up to 1500 RPM. If engine speed responded as commanded within 50 RPM, system is okay. If engine speed did not respond as commanded within 50 RPM, go to step  3.
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