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Home >> Pontiac >> 2003 >> Vibe Base, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - System & Component Testing >> Idle Control Systems >> Idle Air Control System >> Diagnostic Procedures
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Diagnostic Procedures

  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 1.8L VIBE article.
  2. Is there a DTC P0505 set? If yes, go to DTC P0505: IDLE CONTROL SYSTEM under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 1.8L VIBE article. If no, go to next step.
  3. Start engine. Run engine until a normal operating temperature of at least 174°F (80°C) is achieved. Allow engine to idle for at least 15 minutes after reaching operating temperatures. Operate engine at 2500 RPM for 90 seconds. Release throttle and wait 30 seconds while engine idle stabilizes. Observe ENGINE SPEED and IAC MOTOR COMMAND parameters on the scan tool with transmission in Park or Neutral. Are ENGINE SPEED and IAC MOTOR COMMAND within 750-850 RPM (M/T) or 700-800 RPM (A/T) 27-47% IAC Motor Command? If yes, go to step  5 . If no, go to next step.
  4. Operate engine at a normal operating temperature. Select RPM CONTROL, under IAC SYSTEM, in the SPECIAL FUNCTIONS menu of the scan tool. Command IAC valve to increase and decrease engine speed using the scan tool. Did engine speed increase and decrease as commanded by the scan tool? If yes, go to next step. If no, go to step  8 .
  5. Start the engine. Place transmission in Park or Neutral. Operate the following accessories, one at a time, while observing Engine Speed and IAC Motor Command parameters on the scan tool:
    • Turn ON the headlights.
    • Turn ON the rear window defogger, if equipped.
    Did IAC Motor Command increase 1-3%? If yes, go to next step. If no, go to ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS  .
  6. Turn the HVAC blower motor and the air conditioning ON, if equipped. Did the IAC Motor Command increase 4-14%? If yes, go to next step. If no, go to ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS  .
  7. Turn OFF all accessories. Turn steering wheel fully to the right and fully to the left. Return steering wheel to center, straight ahead position. Did IAC Motor Command increase 2-10%, when the steering wheel was turned all the way in either direction? If yes, go to step  16 . If no, go to ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS  .
  8. Turn ignition switch to OFF position. Disconnect IAC valve harness connector. Turn ignition switch to RUN position, engine OFF. Using a test light connected to ground, probe IAC valve harness connector terminal No. 2. Does the test light illuminate? If yes, go to next step. If no, go to step  12 .
  9. Using a test light connected to battery voltage, probe IAC valve harness connector terminal No. 3. Does the test light illuminate? If yes, go to next step. If no, go to step  13 .
  10. Turn ignition switch to OFF position. Using a fused jumper wire, jump IAC valve harness connector terminal No. 2 to terminal No. 2 of the IAC valve. Using a second fused jumper wire, jump IAC valve connector terminal No. 3 to terminal No. 3 of the IAC valve. Connect a fused jumper wire to IAC valve terminal No. 1. Insulate the terminal No. 1 jumper from contact to ground. Start and idle engine. With engine idling, repeatedly touch terminal No. 1 jumper to battery ground with a rapid ON-OFF motion. Does engine speed increase as the terminal No. 1 jumper is rapidly grounded ON and OFF? If yes, go to next step. If no, go to step  14 .
  11. Turn ignition switch to OFF position. Remove all jumpers. Disconnect PCM harness 34-pin harness connector (containing the IAC valve open control circuit). Check terminal No. 1 of the IAC valve open control circuit for a grounded, open, or shorted to voltage circuit. Repair circuit as necessary. Was a circuit repair made? If yes, go to step  17 . If no, go to step  15 .
  12. Locate the cause of no power to the IAC valve connector. See TEST DESCRIPTION  . Repair as necessary. After repair, go to step  17 .
  13. Repair the open IAC valve ground circuit. After repair, go to step  17 .
    14. CAUTION: The IAC valve seals the coolant passage of the throttle body.
  14. Replace the IAC valve. After repair, go to step  17 .
  15. Replace the PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - VIBE article. After repair, go to step  17 .
  16. Turn OFF all accessories. Ensure engine is operating at a normal temperature. Observe ENGINE SPEED and the IAC MOTOR COMMAND parameters on the scan tool with the transmission in Park or Neutral. Are ENGINE SPEED and IAC MOTOR COMMAND within 750-850 RPM (M/T) or 700-800 RPM (A/T), 27-47% IAC Motor Command? If yes, system is okay at this time. If no, go to ROUGH, UNSTABLE, OR INCORRECT IDLE AND STALLING under SYMPTOM DIAGNOSIS in TROUBLE SHOOTING - NO CODES - 1.8L VIBE article.
  17. Use scan tool to clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate vehicle within the Conditions for Running the DTC as specified in the supporting text. Are any DTCs displayed on the scan tool? If yes, go to next step. If no, system is okay at this time.
  18. Operate vehicle within the conditions in which the customer concern was first noticed. Is the concern still present? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 1.8L VIBE article.
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