badboy rs

hi guys

i know this is a ford forum but as there are loads of helpful people on here i thought i might be able to get some clues.
right i have a 1998 merc clk 320 auto, other day i started the car(engine was cold) went down the down road and while i was waiting at the traffic lights, the engine just cut out and it really worried me as it struggled to turn back on again, and the thing is it only does it when you start it from cold, when the car is warmed up, its fine.

any help or clues would be very much appriciated.