My CLK is juddering from cold
 

my car has started juddering - only from cold - (left over night or at work all day). It does this for about 30/40 yards when accelerating then is fine the rest of the journey. Also, it seems to lose power for these 30/40 yards. We are only talking 20 seconds in totalo. If i've been shopping or something for an hour, the car is fine. It is not due a service for 2000 miles and had done 82k in total. It starts first time every time and there are no noises or any other problems. Any ideas?