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New to the forum, but been watching etcg for a while now…best channel ever and I really like the new site 🙂
Construction is my main area of expertise. I’m mechanically inclined but still a noob compared to some of you (so keep that in mind when explaining stuff 🙂
94 Olds Model 98 3.8L
Here’s what I know so far
1) Was driving car like normal several days ago and it fired a MIL then shortly after it stalled (shut off) on me twice while I was driving2) It has one of those stupid OBD 1.5 systems so after researching it I order an ALDL cable and used tunnerpro…hopefully I did everything right but it looks like the error code I’m getting is “122 TPS LOW” (tunerpro also shows live data if that’s helpful)
3) Played with it more and noticed that it stalls every time when I rev it at a constant RPM for a few seconds then suddenly let off the gas
4) There are three sensors near throttle body…one is MAF and I think I got the TPS right? Anyway tested it and it goes from 1K – 5K smooth with no dead spots
5) Also noticed oil and antifreeze around engine…think I have a head gasket fail or worse but I havn’t had time to test it yet…not sure if it has something to do with the stall?
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Also just did one more test on TPS
Back probed the plug
1st wire) 5V constant
3rd wire) .04V constant
2nd wire) first went from .2V-2V when open/close throttle. Then it stopped doing that and went from .13V-1.2V consistently…I used max/min function to get that and didn’t see any negative values or anythingPic of three plugs
All the way to right is MAF
Bottom – TPS
Above that idk?What is that other sensor and could it have anything to do with the problem
Stalling on letting up on the gas can be caused by a stuck EGR valve. Does your car have one of those?
Not sure where it is :blink: …could it be what you see in the center there know it doesn’t have the disc shape but it does have one hose going from exhaust and another going to the intake???
see if this helps with the tps.
http://easyautodiagnostics.com/gm_tps_3.8L/troubleshoot_bad_tps_1.php
[quote=”college man” post=74736]see if this helps with the tps.
http://easyautodiagnostics.com/gm_tps_3.8L/troubleshoot_bad_tps_1.php%5B/quote%5D
That site is really awesome thanks!…hopefully I’ll have time tomorrow to run that test
how does it idle? just thinking of possible vacuum leak. throttle plate closed, it gets a sudden rush of unwanted air, something to check anyways, it would have to be pretty severe though to kill it. can’t think of the name right now, but check the idle control motor dealy. IAC? doesn’t sound right, rough night. for now, its called the dealy. now idle air control does sound right, that’s probly the part you are questioning.
[quote=”shaun” post=74793]how does it idle? just thinking of possible vacuum leak. throttle plate closed, it gets a sudden rush of unwanted air, something to check anyways, it would have to be pretty severe though to kill it. can’t think of the name right now, but check the idle control motor dealy. IAC? doesn’t sound right, rough night. for now, its called the dealy. now idle air control does sound right, that’s probly the part you are questioning.[/quote]
Thanks for the reply, yes I think it does have to do with air flow (sensor to be exact)…
Here’s the verdict…I used college man’s website link to first test the EGR it read .7V which passed so I didn’t remove it to test further
Next I tested the TPS…it had its 5V signal, and ground, the other wire read 0.2V-2V not 0.4V-5V like it’s supposed to (it does however vary it’s resistance smoothly which is a good sign so kind of weird it’s bad)
Anyway, I’m ordering a TPS and will try and report back if it fixes the problem! Thanks to everyone!
Yeah that looks like an EGR valve. I would try to pull it off and see if the valve closes properly. They often get rusty or Carbon packed.
As with anything near the exhaust manifold, the bolts may be rusty or annealed so they may be hard to remove without rounding off the heads. Use a good 6 point socket or wrench on the bolts.
[quote=”grg88″ post=74810]Yeah that looks like an EGR valve. I would try to pull it off and see if the valve closes properly. They often get rusty or Carbon packed.
As with anything near the exhaust manifold, the bolts may be rusty or annealed so they may be hard to remove without rounding off the heads. Use a good 6 point socket or wrench on the bolts.[/quote]
Thanks, yeah I did test it and it tested ok
Here a small update: pulled out the tps messed with it moving it through it’s full range of motion, eventually put it back in and my problem stopped. It reminded me a lot of erics video on a sending unit (which is same potentiometer type device) once he took it out and put it back in it worked fine.
However, I’m going to just replace it ($50) since stalling while driving is a safety issue
Thought I’d post my findings for anyone coming across this thread.
TPS was in fact bad…The old and new TPS had similar resistance ranges. However, when plugged up the signal voltage varied a lot. The old went from .2-2.3V the new one goes from .5-4.5V (thinkin my gas mileage will be a lot better now)
Also, after looking closer and using OCT radiator leak tester (model 7991) which is an awesome product, I realized that antifreeze was very slowly leaking out of my throttle body onto the TPS causing it to fail.
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