South East Events Moderator
Sounds very much like the pre cat lambda sensor. Mine has seen better days so I'm in the process of replacing it.
Got pretty much the same symptoms- works alright once warmed up, but first start every morning it's very rough- usually high revving at about 1200-1400 rpm. After a few miles at idle it goes back to about 800rpm. I got mine diagnosed on VCDS which highlighted the problem. Bit of a bugger to change I've been told so I'll be leaving it to the professionals to fit it! Lol