Hi All
so thats what i am....a judderer.
I had posted a question on the A6 forum about a vibration at 1600 to 2000 RPM and then came across this thread and it seems i have the same problem on an 1.9 tdi A6.
The uneven idle isnt bad and is tolerable but the judder at about 1600 to 2000 RPM bugs the hell out of me.
i'm really only starting out trying all the things mentioned in this thread and others and still have some hope that maybe one of them will fix my problem.
The only things i've noticed that are in any way different are that turning on anything that draws a bit of power like headlights or heated rear window improves the problem and the problem is definitely less noticeable when the weather is warm.

Originally the fact that it was always there and was there at a specific RPM range had me worried that it was something mechanical in the engine but if it was mechanical the engine would have shredded itself by now.