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HOMESERVICE MANUALSGMC1995PICKUP C2500, 2D PICKUP, 7.4 N, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTS - 7.4LFUEL SYSTEMIDLE CONTROL SYSTEMIDLE AIR CONTROL (IAC) VALVE
1995 GMC Pickup C2500, 2D Pickup, 7.4 N, Automatic

Idle Air Control (IAC) Valve

1995 GMC Pickup C2500, 2D Pickup, 7.4 N, AutomaticSECTION Idle Air Control (IAC) Valve
  1. 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.
  2. 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/PCM/VCM output devices (bidirectional) or a special IAC Driver and Noid Light Set (222L or J-37027). Flow charts in TESTS W/CODES - 7.4L article may refer to Tech 1 tester, General Motors' bidirectional tester.
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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.