Cenwesi,
Your problem sounds similar to mine. I have a 95 ls and in the last few months it happened 3 times that my motor stoppd. Similar situation each time; after a long drive (highway) I leave the highway and brake to stand still. Normally the RPM drops to around 500 RPM (A/C on between 500 and 750). In these cases; the RPM needle drops till ZERO....and the motor shuts down (logical). Put the gear in N, start again and no problem, no hesitation (in my case).
The dealer picked up the car, checked it completely (technically, computer, logs and so on) but couldnt find a solution. Maybe, they said, ih has something to do with some part of the fuel "system" which somewhere disturbes the fuelsupply or maybe something needs cleaning like Colin says.
My dealer spent a day on the car and I know they are very strict and well trained / ecquiped....
Since october it happened once. If it is gonna happen more often or when it creates unsafety (no motor runing means no brake- or steering assist) I will have it picked up and checked again.
Sounds like your problem? Coz I think I redue my chances of motor quitting by always have A/C switched on (i didnt have it on always, now I do)
Greets,
Speedy J