Hi, my 07 plate A6 2.0L TDI S Line has started rocking and revving at idle. This happens in drive, park and neutral, is intermittent and has only started happening since its last service and cam belt change. Have taken it back to the garage 4 times now. Each time they say it's nothing that they've done and so the problem remains. I've changed fuel filter, the cam timing is supposedly ok.. So I'm stuck! Any ideas or advice greatly appreciated! Thanks!