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Home >> Chevrolet >> 1999 >> Tracker 2D Utility, 1.6 6, 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Engine Component Tests >> Idle Control System >> Engine Control System & Engine Component Tests >> Idle Air Control (IAC) System Diagnosis
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Idle Air Control (IAC) System Diagnosis

  1. 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 and warm engine to normal operating temperature. Using scan tool, observe IAC duty. If IAC duty is 20 percent with 147 L/min., go to step  6 . If IAC duty is not 20 percent with 147 L/min., go to next step.
  3. Using DVOM, measure resistance between the following IAC valve internal circuits. See appropriate wiring diagram in WIRING DIAGRAMS article.
    • Terminals No. 1 (Purple/Black wire) and No. 2 (Blue/Black wire)
    • Terminals No. 3 (Light Green/Black wire) and No. 2 (Blue/Black wire)
    • Terminals No. 4 (Gray/Blue wire) and No. 5 (Blue/Black wire)
    • Terminals No. 6 (Purple/Yellow wire) and No. 5 (Blue/Black wire)

    If resistance is 35-43 ohms, go to next step. If resistance is not 35-43 ohms, replace IAC valve.

  4. Install scan tool. With engine idling at normal operating temperature, turn A/C on. If IAC duty is 36 percent with 136 L/min. and 800-820 RPM, go to next step. If IAC duty is not as specified, diagnose A/C circuit. See appropriate MANUAL A/C-HEATER SYSTEMS or AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
  5. With engine idling at normal operating temperature, turn A/C on. Disable headlights. Using scan tool, observe IAC duty. If IAC duty is 19 percent with 136 L/min. and 750-770 RPM, go to next step. If IAC duty is not as specified, diagnose A/C idle circuit. See A/C IDLE CIRCUIT DIAGNOSIS  under MISCELLANEOUS CONTROLS.
  6. With engine idling at normal operating temperature, using scan tool, observe MAF sensor, HO2S and TP sensor operation. If sensors are within proper operating range, go to next step. If sensors are not within proper operating range, diagnose sensor. See appropriate sensor under ENGINE SENSORS & SWITCHES  .
  7. With engine idling at normal operating temperature, place transmission in Reverse or Drive. Using scan tool, observe IAC duty. If IAC duty is 27 percent with 187 L/min. and 700-720 RPM, go to next step. If IAC duty is not as specified, diagnose transmission range switch. See TRANSMISSION RANGE SWITCH  under ENGINE SENSORS & SWITCHES.
  8. With engine idling at normal operating temperature, turn steering wheel to the left, and then to the right for more than one turn. If engine RPM changes, go to next step. If engine RPM does not change, diagnose Power Steering Pressure (PSP) switch. See POWER STEERING PRESSURE (PSP) SWITCH CIRCUIT DIAGNOSIS  under MISCELLANEOUS CONTROLS.
  9. Check Positive Crankcase Ventilation (PCV) system. See POSITIVE CRANKCASE VENTILATION (PCV)  . Repair as necessary. If PCV system is okay, go to next step.
  10. Check fuel pressure with engine running. If fuel pressure is 30-37 psi, go to next step. If fuel pressure is not 30-37 psi, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  11. Operate vehicle within conditions under which original symptom was observed. Using scan tool, retrieve DTCs. If no DTCs are set, system is okay. If any DTCs are set, perform appropriate DTC test. See appropriate SELF-DIAGNOSTICS article.
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