I am currently having starting problems with my 1999, Audi A6 Quattro. After taking my car to a shop I was given an error code that would point me in the direction of the problem, but I'm not sure what to make of it.
It was error code P0322, no signal on the ignition/distributor engine speed input electrical circuit for a predetermined period of time.
Probable causes: 1) Poor Electrical Connection 2) Faulty Knock sensor (Was told not likely to be the problem)

The problems started a couple months ago when my car would fail to start on rare occasions, but given 30 minutes or so it would start right up without a problem. However, as of a few days ago, the problem started to occur quite often leaving me stranded wherever I had parked. Now it is sitting in my driveway and I am not sure where to continue on from here.