I know there are others who've experienced this problem before, but after considerable searching, I'm at my wits' end. I started my 89 yesterday, and it bucked and sputtered to life. I read a code 22, and changed the TPS since I had a new one anyway. It didn't help. I've done this before, and calibrated it, but unfortuneately, I've forgotten the calibration procedure (I forgot which wires to probe with the multimeter and under what conditions) Even after tilting it counterclockwise to increase its idle voltage, I still get 22. Only 22. I checked the plugs, and they're black (running rich) but not gummed. I checked the fuel pressure and waited for it to "bleed down," and everything seemed to perform properly. I don't know if it's the ECM or the wire (blue). Now, the car won't even run long enough to get it off the ramps, and the RPM shoots through the roof (surges) when I stab the throttle to keep it running. Any input would be greatly appreciated.

 

Of course, the error codes should be cleared after resetting the TPS so that the stored code does not get reported, even though the problem may have been repaired. That code will remain for the next 50 engine run cycles, so it needs to be cleared.

If the problem repeats after your adjustment, you need to verify that the TPS has the correct reference voltage across the 'A' and 'C' terminals.

The TPS 'A' terminal is the ECM reference ground, which should be at the same potential as any good engine ground. With power off, you should be able to measure the resistance between the 'A' terminal and a good ground, and read 0 ohms. If you have more than half an ohm, you need to check the ground connections at the right rear of the engine, battery, ground node on the body, and at the ECM.

The TPS 'C' terminal should have a constant +5VDC with respect to ground ('A' terminal) whenever the ignition is on. This voltage is supplied by the ECM logic voltage regulator, and is crucial to correct sensor inputs. If the voltage is low, the TPS signal back to the ECM will always be low. If you meter less than 4.9VDC, you need to check the connections between the ECM and the TPS connector.

If the reference voltage is correct at the TPS connector, back-probe the connector and meter the TPS between the 'A' terminal (ground) and 'B' terminal (TPS output) and adjust the position of the TPS to obtain 0.54VDC. If the ECM still reports a '22' after this, you need to check the connection between the TPS 'B' terminal and the ECM.

 

Vader: Thank you very much for the input. Your explanation is better than any of the books I have read. I fixed the car, but it was quite by accident. You may have heard this particular story before, but if you have a minute, please humor me and read this. When I changed the TPS, and subsequently the ECM, the problem still persisted. I did the latter of those two things between the time I last posted, and this response. I was just about to tear into the wiring, and just on a hunch, I went ahead and changed the Mass Airflow Sensor. I had a stock one lying around that I had purchased a couple of years ago that I had changed the fine mesh screens to ones of a larger mesh. Sure enough, the problem disappeared, as did the code 22. Here was my, obviously flawed, line of logic: Code 22 is a TPS problem, but if the TPS isn't the problem, then perhaps the device reading the input is (the ECM). I was wrong. In hindsight, this little fact may have been a giveaway: The car was running "pig rich." I had pulled a spark plug and it was black, indicating a rich condition. I still can't figure out why: (1) code 22 set in the first place, and (2) why a MAF code didn't set at all, and (3) why I didn't think to change the MAF when I saw the TPS reading low, and the car was running rich anyway. Dare I say WTF???? Go figure.