With ignition off, disconnect carburetor connector and check resistance between terminals "A" and "C" in carburetor side of connector. See Fig 1 .
If greater than 7000 ohms of resistance is present in step 1), check for open in harness or poor harness and terminal connections. If harness and connections are okay, replace TPS.
If resistance is less than 3000 ohms in step 1), check for short in harness. If harness is okay, replace TPS. If resistance is 3000-6000 ohms step 1), place ohmmeter between terminals "B" and "C" and ensure resistance decreases while opening throttle.
If resistance did not change in step 3), check for open in harness or poor harness and terminal connections. If harness and connections are okay replace TPS.
If resistance did decrease in step 3), TPS is okay. Check idle switch operation by checking resistance between terminals "C" and "D" at idle position. If resistance is zero ohms, go to step 6). If resistance is not zero ohms, check for open wire of idle switch. If idle switch wire is okay, adjust or replace idle switch.
While opening throttle, ensure resistance increases to greater than 100 ohms. If resistance does not increase, check for short of idle switch wires. If idle switch wires are not shorted, replace TPS assembly.

Fig 1: Throttle Position Sensor/Idle Switch (Spectrum)

Courtesy of GENERAL MOTORS CORP.

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.

Safety Warning

Throttle Position Sensor (TPS)/Idle Switch (Spectrum)