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B-5: Idle Air Control Valve System Check: Aerio

  1. Check engine idle speed and Idle Air Control (IAC) duty cycle. See IDLE SPEED & MIXTURE in ON-VEHICLE ADJUSTMENTS article. If idle speed is within specification, go to next step. If idle speed is not as specified, go to step  4.
  2. Turn headlights, heater blower and/or rear defogger on. If idle speed stays within specifications, system is okay. If idle speed drops below specification, go to step  4.
  3. Check air intake system for leaks or clogging. Also, check fast idle plunger adjustment. See COLD (FAST) IDLE under IDLE SPEED & MIXTURE in ON-VEHICLE ADJUSTMENTS article. If no problem is found, go to next step. If problem is found, repair as necessary. After repair, retest system.
  4. Check IAC valve operation. See IDLE AIR CONTROL VALVE OPERATION CHECK in SYSTEM & COMPONENT TESTING article. If no problem is found, go to step  15. If problem is found, go to next step.
  5. Measure resistance between IAC valve terminals. Resistance should be 8.6-10.6 ohms at 68°F (20°C). Measure resistance between terminals and IAC valve body. Resistance should be infinity. If resistance is as specified, go to next step. If resistance is not as specified, clean or replace IAC valve as necessary. After repair, retest system.
  6. Check A/C input signal to ECM. See A/C SIGNALS CIRCUIT CHECK under MISCELLANEOUS CONTROLS in SYSTEM & COMPONENT TESTING article. If no problem is found, go to next step. If problem is found, repair as necessary. After repair, retest system.
  7. Check for malfunction in following systems:
    • High accessory engine load.
    • EGR valve malfunction.
    • EVAP system malfunction.
    • Engine mechanical malfunction.
    • Throttle position sensor malfunction.
    • Engine coolant temperature sensor malfunction.
    • PCV system malfunction.
    If no problem is found, go to next step. If problem is found, repair or replace as necessary. After repair, retest system.
  8. Check engine idle speed and Idle Air Control (IAC) duty cycle. See IDLE SPEED & MIXTURE in ON-VEHICLE ADJUSTMENTS article. If idle speed is within specification, testing is complete. If idle speed is not as specified, check for clogged idle air passages. If problem is found, repair as necessary. If no problem is found, substitute ECM with known good unit and retest system.
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