98 A6 Q.

Issues -
The RPMs will jump between 1 and 3 several times then, the car will then drive rough, and die. If I try to restart the car it won't turn over. I tried starting the car the next day and it is fine. This is frustrating. Sometimes it takes several days before the car will run again.
I would like the car to be more reliable.

It has done this several times and the shop says they can't find the problem if the car is not having issues when I bring it in.

Any ideas what the issues could be or what to do to begin looking for the issue?

 

Check the ground cable between the frame and motor.
Don't just make sure it is tight.
Remove both ends - clean the surfaces and reinstall.

 

I will try that and see if the issue returns. Thanks for the idea.