The throttle position sensor (TPS) on a Pontiac Fiero is a potentiometer used by the computer to determine the amount and rate of throttle opening. The sensor sends a voltage of less than one volt at rest and when advanced to the open position, the resistance declines and the voltage correspondingly increases. This increase and rate of increase is sensed by the computer, and in conjunction with other sensors, the computer correlates a plan of action to produce the desired result in the form of engine performance. The Fiero is strange in that some of the throttle position sensors have bolts that are welded and require a replacement of the throttle body in the event of a sensor failure. A few have sensors that are not adjustable. If they are adjustable, the holes will be elongated.
Remove the air cleaner and air tube to the throttle body.
Test the sensor for the correct signal. The sensor has a three-wire connector. The dark blue wire is the sensor signal. The gray wire is the PCM (+5V) from the computer. The black or orange wire is the PCM (-) to ground. Connect the voltmeter to the dark blue signal wire and the other lead to ground. Turn on the ignition and the voltmeter should show less than one volt. If more than one volt, the sensor must be adjusted if possible or replaced if not. If there is no signal, connect the red lead from the voltmeter to the black or orange wire (PCM-) and the other lead to ground. The voltage should be less than 100mv. If higher, the TPS is bad.
Adjust the TPS for voltage that is high or out of range. Use the ¼-inch drive ratchet and the appropriate torx bit and loosen the two screws on the side of the TPS. Attach the voltmeter with the red lead connected to the TPS signal wire and the other lead to a good ground. With the key on, the target voltage is 0.5 volt. Rotate the TPS either way and watch the voltage. When the voltage is 0.5 of a volt, tighten down the screws. If the voltage is not obtainable, replace the TPS and re-adjust.
