I have had that exact same issue for a bout 2 years now! The only responses posted have been 'tranny software issues', and 'maf sensor' bad as Big J has said.

I replaced the MAF sensor but still it persisted. I haven't done the software upgrade-1. Because it will cost £££'s as mine is an '01 with no warranty, 2. Because so many people have said it has made no difference, and there never seems to be a conclusion by anyone to say it fixed the problem, therefore it couldn't have been the root cause. 3. I don't believe its to do with my tranny as its as smooth as a baby's arse-damn near as good as a Merc!

So, thanks Big J I will look at the air idle control valve, that one hasn't come up before. (any pointers as to where it is?)

o.l.t, even though I share your experience I have put up with it for 2 years now (had the car 3yrs), I just put my foot down enough to get rid of the surging but not too much that I'm driving hard from cold-I'm sure you know what I mean. I hope you get it sorted, and thanks for bringing this up again, I'll have a look at the air idle valve and report back my findings.

Good luck with yours!