I have a 2001 Cabrio that spits and sputters when it gets warmed up, it seems like alternator is acting up also, the dash lights suddenly get dim and it seems that's when the sputtering begins and then it suddenly goes back to normal.
I am wondering if a bad alternator or voltage regulator could cause this?
Thanks.

 

You need to get your motor scanned (preferably with VAG-COM\VCDS) for any error codes logged in the ecu and post them, that will save a lot of guessing.