Need help interpreting OBDI codes for my 92 Lesabre

OptimistPrime

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I recently posted about how my 92 Lesabre was having trouble running right after extended driving. After 60+ miles it seems to have no acceleration, and the problem gets progressively worse until the car barely drives at all. Then once it cools down overnight, it's fine again. After replacing an O2 sensor, the car drove great... for a couple of weeks. Then today I drove about 120 miles, and on mile 110 it started doing the same thing again. Only this time, I know how to read the scan codes with a paperclip. Never had to do that before, but I'm stumped at this point. So here are the codes:

Code 21 Throttle position sensor error (signal high)
Code 22 Throttle position sensor error (signal low)

How can it be both high and low? If the TPS was messed up I would expect it to stall more. It hasn't stalled once so far on this issue.

Code 31 Gear Position Switch (PRNDL) error

That code can also apparently correspond to a wastegate error on turbo cars, but my car has no turbo. It also has no indicator needle on the trans shifter, it fell off. Maybe that's what the code is talking about? How do I fix this?

Code 58 Trans fluid temp sensor circuit error (low voltage) / VATS system error

This is another one where I have no idea how to fix the thing it's talking about. I guess a good starter question would be where can I find the line for this sensor, so I can examine to see if it got corroded? Is it possible the trans fluid simply becomes too hot and the car won't get into gear? Because it seems to shift fine, even with the problem.

So those are my codes. Any help is appreciated. I realize not all of these are going to be related to the issue at hand. Right now I'm just trying to narrow it down.
 

OptimistPrime

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The codes in the link below are vehicle specific for the '92 VIN-L LeSabre, along with some tips on what to check.

92-93 3.8L VIN L

Part 1 -How to Test the GM 3.8L Throttle Position Sensor (TPS)

Thanks. Going down the list, it seems I must have a fault in the wiring between the ECM and the TPS. That's the prognosis for both code 21 and 22. For 31, it says my Park Neutral Position switch has a fault. I wonder if this might relate to a condition the car had last year, where it would get stuck in park. I would have to turn the car off and back on to make it work right, iirc. Thankfully it stopped doing that after a while.

The code 58 seems to indicate something is wrong with my immobilizer control module. I take it this is the security system, and won't affect drivability. Probably not a priority to fix that. NO ONE is going to steal this car, trust me.

I wonder if that TPS wire fault might be near the pigtail. I had an O2 sensor pigtail go bad in my truck, and it looked fine externally. However on the inside the wire was all corroded and green. I think my next steps will be to troubleshoot that wiring and perhaps put a new pigtail on it, if no damage is visible elsewhere. This is almost certainly a TPS problem, considering the trouble the car has with accelerating.
 

Homer Jay

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Could be ignition issues that are triggering codes.
Given the symptoms, have you replaced the wires and plugs? Also the ICM could be at fault since the problem appears when the engine gets hot. Electronic components can be fine when cold, but malfunction when hot.
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imidazol97

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The throttle position sensor can be checked with an ohmmeter for smooth operation
as it goes from minimum to maximum. The only problem here is that it might have
to be checked after it's very hot.

Checking would mean disconnecting the leads and you can check the condition of
the contacts.

A is the 5 volt reference input.
B is the output that will change with position
C is the ground input.
 

OptimistPrime

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Could be ignition issues that are triggering codes.
Given the symptoms, have you replaced the wires and plugs? Also the ICM could be at fault since the problem appears when the engine gets hot. Electronic components can be fine when cold, but malfunction when hot.
The plugs and wires are fairly new, but changing them is one of the next things on my list of stuff to try. The ICM is brand new, and a genuine Delco product. I've changed the ICM a few times in chasing this bug, and at this point I think I can rule it out. I do have a few extra ones I can swap on to try.

Today I examined the wiring up to the ECM, and it all looks fine. I'm going to try splicing a new pigtail on, since the current one looks like crap. I also have more throttle position sensors around here somewhere. So I could swap one of them on to see if it helps.
 

OptimistPrime

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I put a new pigtail on, but this only caused the CEL to turn on constantly. Defective I guess. Cheap Autozone crap. I spliced in a connector I found on a Delta 88 at the junk yard. It doesn't look much better than the one I had to start but at least the light went away. I'm letting the car sit with the battery unplugged to let the codes clear, and then I'll check and see if it gives the same ones or fresh ones.
 

OptimistPrime

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I spliced on the junkyard pigtail and cleared the codes. Drove it around and the CEL came on once for a brief time. Got home and pulled a code 22. So, still TPS issues, but not as bad as before. My next steps will be to change the TPS, get a good OEM pigtail, and if that fails. I'll run new wires to the ECM.
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