Issues Diagnosing Intermittent Stalling Issues (Page 1/1)
Island198 FEB 09, 02:42 PM
Hey all, I have an '86 2.8 automatic I am trying to diag a relatively annoying issue on. Primarily, I am dealing with random engine stalling. It generally does not happen in motion, but will very often happen at stop lights/while parking, during the acceleration out of a stop light, or even just in park while letting her warm up. As long as I am in motion it tends to stay away, and if I drop into neutral at a light and give it just a tiny bit of gas, I seem to be able to stave off any stalling.

I've tried to pour over what I can find online and in books to try and get a diagnoses. I will say I am relatively convinced it has to do with my idle (which is very bouncy in general). I have seen some examples of the TCC going bad and producing slightly similar symptoms, but I don't think that can be the case for me if I can be sitting in park the entire time from a start and still have it stall.

So far I've:
  • Redone all the vacuums lines
  • Re-gasketed the upper intake plenum in the process of that
  • Attempted to check for remaining vacuum leaks, though not extremely thoroughly. (If there is one remaining it would be very small)
  • Opened up the throttle body/taken out the IAC sensor and sprayed everything heavily with carb cleaner
  • Ensured the IAC pintle was not bottoming out, and also ran the car in diag mode to have it reset the IAC


Next on my list was to try a new IAC sensor entirely, but before I continued further I wanted some second opinions on what else might be causing an issue like this? I do have a feeling the searching idle I have and stalling are related, but so far have not really found much of a solution to either. If anyone had any suggestions or ideas I'd be all ears!
fierofool FEB 09, 03:22 PM
If it stalls instantly when going from neutral to drive, the Torque Converter Control (TCC) switch is failing. As an interim test, look on the front of the transmission case and locate an electrical connector. Disconnect it and drive the car normally for two or three days. If the problem goes away, then it's the switch.

Should you have to replace the switch, you will need to remove the side cover of the transmission. Take pictures for reference of routing the wires.

At the same time as the switch replacement, replace the Case Connector. That's the nylon piece that the chassis harness plugs into on the outside and the torque converter control switch connects to on the inside of the transmission. They are old and brittle and will probably break when you remove it to connect the TCC switch. It's extremely difficult to connect the torque control switch wires while the case connector is in the transmission.

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[This message has been edited by fierofool (edited 02-09-2024).]

Island198 FEB 09, 03:34 PM

quote
Originally posted by fierofool:

If it stalls instantly when going from neutral to drive, the Torque Converter Control (TCC) switch is failing. As an interim test, look on the front of the transmission case and locate an electrical connector. Disconnect it and drive the car normally for two or three days. If the problem goes away, then it's the switch.

Should you have to replace the switch, you will need to remove the side cover of the transmission. Take pictures for reference of routing the wires.

At the same time as the switch replacement, replace the Case Connector. That's the nylon piece that the chassis harness plugs into on the outside and the torque converter control switch connects to on the inside of the transmission. They are old and brittle and will probably break when you remove it to connect the TCC switch. It's extremely difficult to connect the torque control switch wires while the case connector is in the transmission.

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In my case I don't think it would be the TCC, because I can shift between park, neutral, drive, and reverse just fine. The stalling happens within the same gear (as in I can start the car in park and it'll stall in park, or I will have the car in drive, stop at a light still in drive, and the car will stall there). I'd be willing to test it to be sure, but I feel like I'd be barking up the wrong tree.
1985 Fiero GT FEB 09, 05:18 PM
Did you replace the EGR tube, it being cracked can cause a hunting idle, also might be the EGR control if it is somehow getting turned on, then that would stall the engine instantly. Maybe disconnect the small elbow vacuum tube connecting to the EGR valve, that will disable the EGR system from turning on, if that is the problem, EGR tube cracked won't necessarily stall it, but can cause jumpy idle.

Also check TPS sensor, check for proper voltage range, as if that is bad, it can cause the a/f ratio to be messed up, and may or may not trigger check engine codes.
Patrick FEB 09, 05:20 PM

A few basic things to suggest to get you started...

Check for Trouble codes

Check ignition timing, making sure the ALDL jumper is in place during the procedure.

Check fuel pressure.
Island198 FEB 12, 07:15 PM
I appreciate the places to start. I still have more to try, but I attempted to look into some stuff I had the time for today to start. All these tests were done in park without shifting.

I tried disconnecting the EGR valve vacuum line temporarily, didn't seem to have any affect on the stalling. I tried to visually inspect the EGR tube, as well as check with break clean. I didn't find any cracks or leaks, though honestly I will still probably take a much closer look when I have more time.

Prior to any other testing I did pull my codes (to ensure I didn't trigger anything new during testing). I will say the only time my check engine light ever goes on is when I make it onto the highway. It will happen pretty much every time without fail, but does not seem to ever trigger otherwise. I did have 2 codes:
  • Code 32 - EGR Vacuum Control
  • Code 33 - Manifold Absolute Pressure (MAP) Sensor

Not entirely sure what to think of the EGR code, it would not surprise me if there are still leaks in the EGR system, though if disconnecting the EGR valve vacuum didn't make any change to my stalling problem I feel like that might just be an entirely separate issue in itself. The MAP sensor code I am willing to look more into if anyone thinks it might contribute to either a hunting idle or random stalling. I will say pretty much all of my electrical connectors need some replacing, the MAP sensor plug included. The MAP sensor plug was seated a little oddly, upon looking at it. I took it out and reseated it a bit more snugly. I have no clue if this change is actually what affected this, but my idle does seem to be slightly cleaned up, or it could easily just be how it wants to run today. Here is an example of my idle nonetheless https://www.youtube.com/watch?v=8kbIUcb6AYw

All that being said, the car still randomly wants to stall. Still will try more things stated above as time permits, but wanted to update with what I found today in case it gives anyone any more ideas.
Stingray92 FEB 12, 07:37 PM
Map sensor is definitely something to look into, if you got a vacuum guage/pump you can test the sensor output. The ecm will adjust fuel input accordingly. Also go through you engine bay grounds. I've eradicated a few gremlins.

Stingray