Throttle Position Sensor

General Information

The TPS is the Throttle Posistion Sensor. If it's bad it may cause your ECM to think that you are moving the throttle. The ECM then tries to increase or decrease the fuel flow to match the (improper) throttle posistion. You could also have a bad IAC (Idle Air Controller) or bad EGR valve.

You can check the TPS by disconnecting the electrical plug on the TPS unit. The ECM will now use a default value. If your idle problems disappears then replace the TPS unit. BTW, the car may be hard to start and _will_ be down on power with the unit disconnected.

From: Lee Brown


The code 22 is set if the voltage from the TPS is less than 0.2 volts for more than 2 seconds while the engine is running. Check the voltage on the wire connected to the wiper terminal of the TPS. It should vary from a few hundreds of millivolts to a little below 5 volts depending on the throttle position, and do this smoothly without bouncing the needle around (if you are checking it with an analog voltmeter).

The problem probably is in the TPS, but check also for a short in the TPS signal wire to ground.

From: Jukka Alve

4 Cylinder Models

I don't have an '87 Fiero manual available to me, but I believe the color codes I'm about to give you should apply for '87. Check your TPS connector to see if it matches the following:

Pin "A"- Grey wire, 5v reference from ECM
Pin "B"- Black wire, Sensor ground from ECM
Pin "C"- Dk. Blue wire, TPS output to ECM

If your TPS matches these color codes, then you would measure pin "C" as described in previous responses (ignition on, engine off, sensor connected, around 0-5v range from sensor, smooth voltage measurements as throttle is adjusted). With the TPS disconnected, if pin "A" of the harness connector is not providing around 5v, or pin "B" is not near 0v, then you may need to check the ECM or wiring.

If the pins and colors don't match this indexing, then you'll likely find the Dk. Blue wire in pin "B" and the Black wire in pin "C". Either way, you want to measure the voltage output at the Dk. Blue wire.

From: Bret Scott

Removal and Installation

Removal - 4-cylinder

The TPS really isn't difficult, IF you take the EGR valve off first. The EGR valve is just attached with a couple of bolts. There is a gasket between the EGR valve and manifold, so you might want to get one of those (Auto Zone stocks them). The TPS on my son's '84 was attached with Torx fasteners. After disconnecting the electrical connector, just undo the Torx screws. I used a set of Torx

I also bought the new TPS at Auto Zone. It was in a Wells box, but is an AC part!! Once you put it on, you have to identify which contacts in the plug have voltage, and then do some jumpering between the TPS and wiring harness. Then there is a calibration to go through, which is just rotating the TPS to achieve the desired voltage with the throttle closed. This also is not difficult, but you definitely need the digital volt meter, and some jumper wires. There are instructions with the TPS.

The new TPS came with new screws, but they were Phillips. I thought the Torx was better, so I reused them. But one broke on installation--the head snapped off. Perhaps that's their safety to prevent overtightening! By the way, if you haven't already done it, you might want to replace the vacuum line to the EGR valve.

From: Earl Zwickey

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