323i dies while running. Please help

1997 BMW 323i suddenly stalled at 70 KM/hour (40m.p.h.) for no obvious reason. Started again after a few minutes. Brakes were functioning throughout. Electricals seemed to be otherwise functioning. Dealers ran diagnostics and could find nothing wrong. Can any one offer suggestions as to causes or how to diagnose a possible fault please ? This has happened about 4 times in 6 months. I've Lost confidence in the car. Thanks in anticipation. Had posted previously but not getting much help.
Cheers :-)

My 2002 BMW 325i is doing the same thing! I had it happen a few days ago and then again this morning. I was going probably less than 40mph -- stuck in traffic. I'd like to get some insight before taking it into the dealership. Any help is appreciated.

If they have an electric fuel pump I would test it's pressure.
They tend to die slowly and at unexpected times.
Mechanical pumps however tent to JUST die in one go (If at all)
Just A quick thought.

Thanks for your feedback. I will check into that. Excuse what may be a dumb question -- how do I know if my fuel pump is electric or mechanical?

What Type?, Good question!
If it is electric you would/should here it clicking when the ignition is first switched on. Secondly it will have its own Fuse in the fuse panel.
If it is Mechanical ?:) check a Haines manual!

fuel pump access port is under the back seat. These has not been a mechanical fuel pump in a BMW for a long, long time. Also, if it is a 1997, go ahead and replace the fuel pump and float access ports...the plastic nipples with the fuel lines attached tend to crack and spew gas under the rear seat!