steviei

My 2002 C220 has developed a fault that I hope someone can diagnose for me. It has done 186,000 miles of which I have done over 60,000. I have found lots of info on the forum but this is my first post.
My car starts fine and idles ok, no noises or leaks. It pulls fine just above tick over. but it is then totally flat until I put my foot down then it pulls really strong but I think maybe a bit noisier than usual. If I try to hold a steady throttle it comes in and out like the throttle is an on off switch. when its properly warmed up its almost back to normal. Also its a lot worse if the ambient temperature is below 10c. Weird. Has anyone suffered anything similar? Thanks for any help