Baffling issue with 1993 Audi 100 CS. Please advise.
 

I have a 1993 Audi 100 CS with about 150k miles on it. Today when I was driving down the highway at about 65 mph, the car suddenly jerked, the rpms started fluttering around 1000, the PRND321 started flashing and there was a really rapid clicking sound coming from the dash. There was no power coming from the engine. When I stepped on the gas, nothing happened and I rolled over the the shoulder, stopped the car and switched off the ignition. For about a minute, when I turned the ignition to get power in the car, the same PRND321 lights would flash and the click was present. After about a minute, when I did the same thing, nothing happened and then I started the car.

This has happened to me in the past, but once it happens, it wouldn't happen again for several months. Today, every time I went above 50 mph, this would happen (about 7 times), so I "limped" home going 45 on the highway.

Any ideas to what this could be and how I can fix it? Thanks!