A common problem which affects the camshaft lobes of VW 1.9PD engines, as used in the mk4 Golf, which causes excessive wear of the cam lobes in the engine. This is caused by using incorrect specification engine oil and / or not keeping up with oil changes.
VW Nut #1: DANG! My mk4 TDi is idling hella-rough dawg!
VW Nut #2: Oh Shit! You put some cheap-ass oil in there man! Are you ready for an expensive repair bill on your chocolate cams?