I have a 1991 Bonneville 3.8L "C" vin engine. 200-250K (odometer dead, speed indicator fine)

Instantly start on hot or cold mornings -- idles perfectly.

It started having frequent random instant shutdowns without warning, while driving, never while idling. Dash lights come on, will always instantly restart in neutral while coasting (on the highway - helps keep me awake).

Letting the engine idle for 15 minutes before leaving for work (used to) generally prevent all engine shutdowns in traffic. This is no longer helpful. It stalls 20-40 times before I can get to work (35 mile trip, most on highway).

Problem 99% reduced if I can make it run more than 20-25 miles.

Sometimes it seemed that the "throttle dance" would ameliorate the situation if it was noticed that the revs were dropping. REPLACED TPS. Worked great -- for a few days.

When the stalls became very frequent, I read the computer and found a TTP? [transmission clutch relay] (3-7 code). This code is not included in my year/model error code list???

It would seem to me that the transmission cannot be locked if your tach indicates a significant loss of rpms without a related significant loss of vehicle speed.

Disconnected the battery for an hour -- cleared computer -- problem rectified -- for a few days. No error codes have recurred even with the increased stalling.
Runs very strong and smooth when running. No chugging or other reasonably expected symptoms -- just instant death, rain, shine, hot, cold. (Replaced thermostat as engine appeared to be running a little cool).

I am a paycheck to paycheck teacher; understand general and vehicle electronics (used to design NASCAR ignition systems in Daytona). Am stumped by this one. Thinking of monitoring crank & cam position sensor for missing pulses; perhaps watch for power loss into crank/cam modules.

Have read of a grounding issue and gas level indicator issue somewhere. Any ideas???

Don't let your children grow up to be... middle school teachers - 10-14hr/day thankless job.

Start by inspecting the battery cables, check both ends. You may have a loose connecting at the ground point, or at the starter

Starter is no problem - starts instantly whenever it stalls. Will run a fresh ground from negative terminal battery to frame and report back.

Thank you...

Check out the techinfo/testing area. There are a few tests in there for testing the electrical system. If the engine is just shutting off like a switch was flipped, then it'* a electrical issue.

I would be inclined to also check out the ICM, to make sure that is good, but that will not act any better usually if the computer is reset, it is finicky no matter what.

I also would suggest moving this thread over to the appropriate section, it is a little out of place here.

I dont know if your 1991 Bonneville has a ground location under the door trim on the drivers side but I did read a post about a Olds that had a problem there. here are some links:

http://www.oldsmobileforums.com/foru...ad.php?t=11791
https://www.gmforum.com/showthread.p...grounds&page=2

Keep us informed

I teach science about 40 miles from home. As the weather is worming up the problem is becoming less frequent. When I'm cruising down the highway at 70 (+) I put it in mutual and it will restart every time, but will frequently still shortly thereafter. The battery, charging circuit and ground wires are good. I have heard (but have not verified) that there are some ground wires located basically under the driver'* seat and may be intermittent due to rust or corrosion.

The stalling is generally represented by instant death yet all accessories, lights, radio etc. continue to function.

Any crazy ideas for such a crazy problem will be given serious consideration and reported upon. This problem appears to be relatively common in Bonnevilles that are 10-20 years old.

I would suspect a bad crank sensor.

I would check those wires under the seat!

I found some more possabilities: Post #9, #10 this thred:
http://www.automotiveforums.com/vbul...d.php?t=913774

My 95 Olds suffers the same problem!

x2 ... Sounds like a bad crank shaft position sensor.