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Home >> Oldsmobile >> 1998 >> Eighty-Eight LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Idle Control System >> Engine Controls - System/Component Tests >> Idle Air Control (IAC) System Diagnosis
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Idle Air Control (IAC) System Diagnosis

  1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES article.
  2. Connect scan tool to data link connector. 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 at this time. If engine speed did not respond as commanded within 50 RPM, go to next step.
  3. Turn ignition switch to LOCK position. 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 IAC circuit between IAC valve and PCM for open. If open does not exist, go to step 10). If open 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, 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 exists, repair as necessary and go to step 12). If problem does not exist, go to next step.
  8. Check for poor connection at IAC valve. If problem exists, repair as necessary and go to step 12). If problem does not exist, go to next step.
  9. Replace IAC valve and 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 and 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 at this time. If engine speed did not respond as commanded within 50 RPM, go to step 3).
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