small problems

Ok I'm having small problems with my 93 Chrysler Concorde.
Basically, when I'm driving, the engine all of a sudden might turn off, so I have to put hte car in neutral, start her up, and put in in drive. Happens like once every couple of weeks.

Then at times, when Itry to turn the car on, it turns on, tries to keep the revs up at idle, then dies. And I try again, same thing. Basically these methods have worked for me to start her up. Let the car stand for 10-20 mintues give it a try. Sometimes takes 30-40 mintues. Or rev at 4-5 thousand while parked, which then will cause it to be able to keep the idle revs.

I went to a Chrysler dealership. Payed $300 bucks to run all the tests, they found nothing. Can anyone help me out?