X5 is chugging at idle amd low speed...

[x5pilot]

Hi all,
My X5 over the last few months (4.4 2004 model) has been surging/chugging at first start, idle speed or when doing very slow speeds <5 mph.
I've checked the oil and there are no engine management lights on. The car has only 52K miles on it.
Has anyone any idea what this might be? I'm bringing it into a dealer next week but am very nervous about what they may say it is!

To summerise, I start the car, and let it idle, gradually the engine will start to surge, chug, throttle in/out - its hard to find the right words!
This action will generally stop if I give it gas and/or start driving.
I have no problems on a warm start or at high speeds.

really appreicate any help or suggestions?
Thanks!