We're on Boost said:

Gee, then all that ThrotPos jitter that you have in log.2026.05.30-01 is probably still there. Hope the new wiring will fix that.

Glad that you found a 4-bolt rear end!

Did you ever put an ordinary shop-type mechanical vacuum gauge on the intake manifold so you could watch to see if it's reading the same as your MAP sensor in the logs?

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I know I'm so excited about that 4 bolt rear end! I got the car for free haha!

I have not yet but that is my next plan when I get my ECU back.

I hope to get the harness ASAP but ohm racing is backed up unfortunately

if it is my engine what would be the next plans because I'm not sure what else to do.

Nii said:

if it is my engine what would be the next plans because I'm not sure what else to do.

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Your engine, you mean like maybe the ring gaps are all lined up or something?
I really don't think that is going to be what's wrong.

For sure the weird ThrotPos and TPS Delta behavior is not the engine's fault.
Did you notice how many TPS Delta spikes there are?
You should bring up the log.2026.05.30-01 and hit Ctrl+Q on the keyboard to no-show all the graphs, and then turn a few of them back on. Just ThrotPos, RawThrotPos, TPSDelta, and maybe RPM.
Change the TPSDelta color to something bright that you can see.

I just now noticed from doing that, that when you have a TPS Delta spike in an area where ThrotPos is staying on 0, you do keep getting changes in the RawThrotPos. (RawThrotPos is a lot more sensitive than ThroPos, and it can go higher or lower, whereas Throt Pos won't go below 0).
Your RawThrotPos is jumping around all over the place the whole time that your ThrotPos is on 0.
Mine doesn't do that. My RawThrotPos stays steady at 32 for almost all of the time that my foot is off the gas. Sometimes 31.
Here's something I think you should do. Temporarily replace your Throttle Position sensor with a fixed resistor. You'd have to first measure the ohms of your TPS with foot off the gas pedal and find a resistor about that size.
If you don't get TPS jitters in your log anymore, then the TPS is the cause, or maybe it is some shaking making the throttle cable go pushie pullie on the sensor. If you do still get jitters, then it must be something in the ecu, or in whatever wire you have between the resistor and the ecu. Then you might be able to eliminate that wire, have the resistor lead go right to the ecu input pin somehow. That should eliminate everything leaving the ecu as the problem.

I was going to say "a fixed resistor or an Evo TPS MD628074" which is what I have, but I see those things cost over $100 now and maybe it won't fit on your throttle body. And really I don't know why a new Wells 5S5242 wouldn't be good enough. That's what Rock Auto sells these days for a 1g TPS MD614327.
What TPS are you using exactly?

We're on Boost said:

Your engine, you mean like maybe the ring gaps are all lined up or something?
I really don't think that is going to be what's wrong.

For sure the weird ThrotPos and TPS Delta behavior is not the engine's fault.
Did you notice how many TPS Delta spikes there are?
You should bring up the log.2026.05.30-01 and hit Ctrl+Q on the keyboard to no-show all the graphs, and then turn a few of them back on. Just ThrotPos, RawThrotPos, TPSDelta, and maybe RPM.
Change the TPSDelta color to something bright that you can see.

I just now noticed from doing that, that when you have a TPS Delta spike in an area where ThrotPos is staying on 0, you do keep getting changes in the RawThrotPos. (RawThrotPos is a lot more sensitive than ThroPos, and it can go higher or lower, whereas Throt Pos won't go below 0).
Your RawThrotPos is jumping around all over the place the whole time that your ThrotPos is on 0.
Mine doesn't do that. My RawThrotPos stays steady at 32 for almost all of the time that my foot is off the gas. Sometimes 31.
Here's something I think you should do. Temporarily replace your Throttle Position sensor with a fixed resistor. You'd have to first measure the ohms of your TPS with foot off the gas pedal and find a resistor about that size.
If you don't get TPS jitters in your log anymore, then the TPS is the cause, or maybe it is some shaking making the throttle cable go pushie pullie on the sensor. If you do still get jitters, then it must be something in the ecu, or in whatever wire you have between the resistor and the ecu. Then you might be able to eliminate that wire, have the resistor lead go right to the ecu input pin somehow. That should eliminate everything leaving the ecu as the problem.

I was going to say "a fixed resistor or an Evo TPS MD628074" which is what I have, but I see those things cost over $100 now and maybe it won't fit on your throttle body. And really I don't know why a new Wells 5S5242 wouldn't be good enough. That's what Rock Auto sells these days for a 1g TPS MD614327.
What TPS are you using exactly?

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I'm not completely sure what TPS I'm using it could possibly be a 2g one for all I know I just had a handfull laying around so I just tried them till I found one that wasn't wonky, haha. I honestly may just buy one new it's one of the few remaining sensors I haven't replaced so maybe I should just buy it new

Nii said:

I'm not completely sure what tps I'm using it could possibly be a 2g one for all I know I just had a hand full laying around so I just tried them till I found one that wasn't wonky haha I honestly may just buy one new it's one of the few remaining sensors I haven't replaced so maybe I should just buy it new

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Google AI says you should use a 1991-1994 1G DSM TPS. "The D-shaft orientation, drive tangs, and bolt spacing on the S90 housing align perfectly with this style of sensor. [1, 2, 3, 4]" and it gives some references to Extreme PSI.

So there's that.

And on Rock Auto, I see these sensors listed for 1991. The Wells 5S5242 is the only one there I would get. Wells is part of NGK lately.

Here's something else - since you are worried about the engine, what numbers do you get when you do a compression test on it? Even if the engine is not running, you could do a compression test on the cold engine and it would be better than nothing. I have compression test numbers from somebody just a few days ago that he got on his DSM with cold engine. The engine has 170,000 miles on it and the numbers are pretty low, but the car starts and runs fine, it just has a lot of blowby during boost. Stock cams though. Anyway, it would be something with cold engine to compare to if you got numbers for yours. He did dry, then wet with a little oil.

We're on Boost said:

Google AI says you should use a 1991-1994 1G DSM TPS.

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Definitely I picked up a new one hopefully that helps the jitter

We're on Boost said:

Here's something else - since you are worried about the engine, what numbers do you get when you do a compression test on it?

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I'll see if I can run some of these tests today if I can squeeze in some time

I'm going to give this a try!

You might want to check and see how much and what is connected to the +5v sensor power. Same for the sensor ground line.

steve said:

You might want to check and see how much and what is connected to the +5v sensor power. Same for the sensor ground line.

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Definitely I will! I suspect that there is a break or an aged wire is the issue. This harness is completely stock and I've had to replace many broken/aged wires. I've tried my best to not have anything power from the ECU. they are all on their own seperate harness or just plug in adapter harnesses the only ones I've tapped are the O2 sensor wiring so hopefully if I replace the 5v up to the new wires that I fixed on the two sensors that may fix it.

I'm also thinking if I should wrap the wire with some extra loom or something to help possibly meditate interference.

Nii said:

I'm going to give this a try!

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I'm glad they got to see the TPS noise in a log. So they know there's noise from something, and they say it's not from anything in the ecu.

Should have this diagram if you don't already. I would post you the whole thing but you won't get the whole 2507 x 1901 pixels in here - you'd get it shrunk to 2000 x something. Would be better to post a link to it where it's full size. Can do that if you want. I just noticed the Hot Rod Coffee Shop site is gone. As far as I know that was the original site for this diagram.

We're on Boost said:

I'm glad they got to see the TPS noise in a log. So they know there's noise from something, and they say it's not from anything in the ecu.

Should have this diagram if you don't already. I would post you the whole thing but you won't get the whole 2507 x 1901 pixels in here - you'd get it shrunk to 2000 x something. Would be better to post a link to it where it's full size. Can do that if you want. I just noticed the Hot Rod Coffee Shop site is gone. As far as I know that was the original site for this diagram.

You must be logged in to view this image or video.

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thank you I greatly appreciate it! I wish I had the whole diagram! if you could email it to me I'd really really appreciate it! [email protected]

Nii said:

thank you I greatly appreciate it! I wish I had the whole diagram! if you could email it to me I'd really really appreciate it! [email protected]

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Ok I emailed it to you, and I also put it in my google Drive, available "to anyone with the link" and here is the link.

We're on Boost said:

Ok I emailed it to you, and I also put it in my google Drive, available "to anyone with the link" and here is the link.

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thank you so much I appreciate it so much!!