I have a 1994 Pontiac Bonneville with a non supercharged 3.8L. It has perplexed several mechanics with an intermitten stalling problem. It just quits for no apperent reason. You can be driving for hours and its fine and then is stalls three or four times in a row. You see the tach drop and then a check instrument chime goes off. Sometimes the engin comes back without having to re-start, sometimes it just dies. In every case it starts right back up like nothing is wrong. You can see the volt meter drop but that might just be the aternator not spinning. The computer, crank angle sensor, ignition module, coil pack, and alternator has been chagned by one shop. Other shops have charged diagnostic fees reporting that they could not make it fail. I personally checked all the grounds including those inside the car. It does have a noisy fuel pump but I am not sure if that is normal or not. I think I have checked all the easy stuff including a leaking vacume line to the fuel injector regulator. Nothing has helped. I suspect the loss of fuel pressure but there is no way to be sure. Has anyone else had a problem like this on a Bonneville or similar C or H body GM.:banghead:

Fuel pressure regulator - I believe there may be a recall on it.

I would check the fuel pressure, make sure the ign switch connector doesn't look overheated, look at the harness from CPS to the ICM.

Let me elaborate a bit :)
I had a '98 with that exact problem - car would stall at random times - frequently at lower RPM's but not always. I was worried about some huge costs to fix it, then I got a recall notice in the mail regarding a problem with the fuel pressure regulators in that year (and others but don't remember the date range). After the regulator was replaced, it NEVER stalled or even stumbled on me.

I could see the regulator causing a stall at idle as it leaked into the vacuum hose which would load the engine at idle or decel, the description above does not seem to match the symptoms, but he should certainly look inside the hose at the regulator for traces of fuel, I would assume with the work done someone "would" have done this, as this is basic diagnostics here.