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Home >> Geo >> 1993 >> Storm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Idle Control System >> Idle Air Control (IAC) Valve
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Idle Air Control (IAC) Valve

  1. Set parking brake. With ignition off, connect IAC Driver from Kit (J-37027) to IAC valve. IAC driver is used to extend and retract IAC valve. Movement of IAC valve is verified by change in engine speed.
  2. Start engine. Note idle speed with transaxle in Park (A/T) or Neutral (M/T). Using IAC driver, extend and retract IAC valve while noting engine speed. If engine speed changes, go to next step. If engine speed does not change, check for plugged IAC passages. Replace IAC valve if passages are not plugged.
    NOTE: If IAC valve is extended too far (less than 700 RPM), engine will stall. If IAC valve is retracted too far (more than 1500 RPM), IAC light may flash several times before engine speed starts to decrease.
  3. Engine speed should change smoothly within a range of 700-1500 RPM each time IAC driver light flashes and IAC valve is extended or retracted. If engine speed changes with IAC driver light operation, go to next step. If engine speed does not change with IAC driver light operation, check for plugged IAC passages. Replace IAC valve if passages are not plugged.
  4. Install Node Light from Kit (J-37027) in IAC valve wiring harness to check IAC valve wiring circuits. Cycle IAC driver. Node lights should cycle Red and Green, but never go off, when IAC valve is cycled and engine speed changes.
    CAUTION: Automatic transaxle Electronic Control Unit (ECU) on 4-speed transaxle may be mounted on left side of steering column. DO NOT  confuse ECU with ECM. ECM contains 24-pin and 32-pin connectors; ECU contains 16-pin and 20-pin connectors.
  5. If node lights operate correctly, go to next step. If node lights do not operate correctly, check for defective connections, open wiring circuits and faulty ECM. ECM is located under left side of instrument panel, left of steering column.
  6. Using ohmmeter, check resistance between terminals "A" and "B" (Brown/Yellow and Brown/Red wires) and terminals "C" and "D" (Brown/White and Brown/Black wires). Resistance should be 40-80 ohms. If resistance is correct, go to next step. If resistance is incorrect, replace IAC valve.
  7. Using ohmmeter, check continuity between terminals "A" and "D" (Brown/Yellow and Brown/Black wires) and terminals "B" and "C" (Brown/Red and Brown/White wires). If continuity does not exist, go to next step. If continuity exists, replace IAC valve and retest.
  8. A slow or unstable idle may be caused by a system problem that cannot be overcome by IAC valve. If problem still exists, idle problem may be caused by:
    • Vacuum Leak:  If high idle exists, stop engine. Using IAC driver, fully extend IAC valve. Start engine. If idle speed is greater than 800 RPM, check for vacuum leaks.
    • System Too Lean:  If air/fuel ratio is too lean, idle speed may be too high or too low and disconnecting IAC valve may not help. Scan tester or digital voltmeter (10-megohm) will indicate an oxygen sensor output less than 300 mV (.3 volt). Also, check for low fuel pressure or water in fuel.
    • System Too Rich:  If air/fuel ratio is too rich, idle speed will be low and scan tester will usually indicate more than 80 counts. System may exhibit Black exhaust smoke. Scan tester or digital volt-meter (10-megohm) will read an oxygen sensor output greater than 800 mV (.8 volt). Also, check for high fuel pressure or fuel injectors leaking or sticking. A silicone contaminated oxygen sensor may cause slow sensor voltage changes, resulting in a rich condition.
    • Throttle Body:  Remove IAC. Inspect bore for evidence of IAC valve binding in bore.
    • IAC Valve Connections:  Check for corroded or loose connections.
    • PCV Valve:  Incorrect PCV valve may cause incorrect idle speed.
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