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4-Cylinder Idle Mixture: Pickup

  1. Start engine and warm to normal operating temperature. Run engine at 2000 RPM for 2 minutes. Perform self-diagnostics. See appropriate G - TESTS W/ CODES article in the ENGINE PERFORMANCE section.
  2. Locate ECM. See ECM LOCATIONS table. With idle speed and ignition timing correctly set, increase engine speed to 2000 RPM for 2 minutes. If Green LED on ECM does not go on and off more than 5 times during a 10 second period, go to step 4).
  3. If Green LED goes on and off more than 5 times during a 10 second period, enter and set self-diagnostic system to Mode II. Red and Green LEDs on ECM should blink simultaneously. If both LEDs blink, idle mixture is correct. If both LEDs do not blink simultaneously, go to step 6).
  4. Turn off engine. Disconnect negative battery cable. Disconnect oxygen sensor and ECM wiring harness connector. Using a jumper wire, ground oxygen sensor wiring harness connector. Check continuity between terminal No. 19 of ECM wiring harness connector and ground.
  5. If continuity exists, remove jumper wire. Reconnect ECM and go to next step. If no continuity exists, repair wiring harness. After repairs, reconnect negative battery cable. Recheck idle speed and ignition timing.
  6. Disconnect engine coolant temperature sensor. Connect a 2500-ohm resistor between engine coolant temperature sensor wiring harness. Disconnect Pulse Air Injection System (PAIR) valve hose. Reconnect negative battery cable.
  7. Start engine and warm to normal operating temperature. Increase engine speed to 2000 RPM, 2 or 3 times and return to idle. Check CO% level at idle speed. See 4-CYLINDER IDLE SPEED & CO% LEVEL  table under 4-CYLINDER IDLE SPEED. Remove 2500-ohm resistor from engine coolant temperature sensor wiring harness and reconnect sensor.
  8. If CO% level is incorrect, go to next step. If CO% level is correct, replace oxygen sensor. Start engine and increase engine speed to 2000 RPM. Ensure Green LED on ECM goes on and off more than 5 times during a 10 second period with engine running at 2000 RPM. If Green LED does not perform as indicated, go to next step.
  9. Ensure all components and wiring harness connectors are connected. Perform self-diagnostics. See G - TESTS W/ CODES article in the ENGINE PERFORMANCE section. If no fault codes are present, check fuel pressure, airflow meter, injectors and engine coolant temperature sensor for faults. If all systems are operating correctly but idle CO% level is still incorrect, replace ECM.
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