VW Jetta - Starts ok but it cuts out at idle rpm?

Hi all,

i have a vw jetta, 09 reg, which will start fine but cut out immediately, unless i press the accelerator to up the revs, she will keep running. As soon as I take my foot off the accelerator and the car drops to idle, it cuts out.

Update, when up the revs, say around 3k rpm and hold it there, the car drops revs itself and then runs back up to 3k.

Any ideas?

Thanks