Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1987STEP VAN P20, 7.4 W, AUTOMATIC, 400/M40REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 14 (ENGINE CONTROLS - SYSTEM/COMPONENT TESTS - GASOLINE)FUEL SYSTEMIDLE CONTROL SYSTEMIDLE AIR CONTROL (IAC) VALVE
1987 Chevrolet Step Van P20, 7.4 W, Automatic, 400/M40
Idle Air Control (IAC) Valve
1987 Chevrolet Step Van P20, 7.4 W, Automatic, 400/M40SECTION Idle Air Control (IAC) Valve
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
- Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". See Fig 1. Resistance should be 40-80 ohms. If okay, go to next step. If resistance is not as specified, replace IAC valve.
- Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC valve.NOTE: Functional testing of Idle Air Control (IAC) valve requires a scan tester capable of cycling ECM output devices (bidirectional) or a special IAC Driver and Noid Light Set (222L or J-37027). Flow charts in appropriate TESTS W/CODES article may refer to Tech 1 tester, General Motor's bidirectional tester. See CODE 35 chart in appropriate TESTS W/CODES article for further IAC testing.
- G - TESTS W/CODES - 4.3L
- G - TESTS W/CODES - 5.0L
- G - TESTS W/CODES - 5.7L
- G - TESTS W/CODES - 7.4L
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.