I just got a 99 A6 and the cruise controll will work every now and then but usually doesn't. anyone have any advise? thanks

 

I have the same problem, just finished a 12 hour trip to Montreal and back, every time it crapped out it was time for the wife to drive... I read somewhere in here that the stock is weak.

 

I just read on a website that this may something to do with vaccum servos. Have you checked that?

 

I had similiar problem, it is not as bad as yours I guess. (I ve got 99 A6 too)
I have read in this forum that I think it is a electrical contact problem with the cruise control buttons. I may be wrong but I srongly believe that this is the reason.

Ozzy