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 MANUALSPONTIAC1990GRAND PRIX STE, 3.1 VREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSIDLE CONTROL SYSTEMIDLE AIR CONTROL (IAC) MOTOR
1990 Pontiac Grand Prix STE, 3.1 V
Idle Air Control (IAC) Motor
1990 Pontiac Grand Prix STE, 3.1 VSECTION Idle Air Control (IAC) Motor
- Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". Resistance should be 40-80 ohms. See Fig 1. If okay, go to next step. If resistance is not as specified, replace IAC motor.
- Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC motor.
NOTE:
Testing Idle Air Control (IAC) motor requires a "Scan" tester capable of cycling ECM output devices. Flow charts in the TESTS W/CODES articles may refer to the Tech 1 tester, General Motors' version of this 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.