1994 Volkswagen Jetta Unexplained problem

This is what I would suggest. The problem needs to be addressed when it is present, thus the Dealer's dlemma short of guessing. Which is what I would be doing since it isn't happening.

So, You seem like you can predict this occurance according to this statement:

"The problem I have is this: in the mornings, I can start the car with no problems. If I drive it for about twenty minutes then park and then try to start it again within about a half hour, the motor just won't turn over. It sounds like it is out of gas. Then, if I wait about 15-30 minutes, the car starts up just fine. Lately, the car has even stalled while running and then I have not been able to restart it again for about 30 minutes."

So you need to talk to the service manager and talk to him about your special circumstance that pits you in a postion of needing testing at a particluar point. You set up an appointment and drive it to set the conditions needed and take it in and keep it running until the techs are ready, then shut it off. Hopefully it doesn't start and they can verify the source.

It's kind of a broad spectrum. Anything that is affecting spark or fuel will cause this. I can name many parts that may be responsible, but it needs testing. Carry a fuel gauge and spark tester to start narrowing down the problem.

You can shoot some carb cleaner in the throttle body and see if it starts to put you onto the fuel los path as well.