94 Concours motor dies

[Caddie fan]

What could be causing this fine machine to just quit running while I am driving. At first it was just as I was coming up to a stop which was not a big problem. All I had to do was stop, shift into Park, restart the motor, and go on my way.
Yesterday the thing died while I was going 45 mph down a curving causeway, now big problem which could have been worse!!!!!
My mechanic said there were no codes stored in the computer so he didn't know what was going on.
Anyone have this problem before and had it corrected?
Art