On my 2.3T CSE auto I have a vibration at idle. At first I thought is was probably the plastic undertrays/front spoiler as I'd not replaced all the corroded jacknuts. Anyway ordered new stainless jacknuts and bolts from RS did all the undertrays and front spoiler including having to remove front bumper cover and still the vibration is there at idle - if engine speed increased it goes away. Had a look at engine this weekend when changing oil and filter and saw that its the aux belt tensioner that is vibrating allowing the pully its attached to to jump about a couple of milli or so. Guess it means a new tensioner (car has done 107k) has anyone come across this before?