Won't idle runs like one cld until you make her pull a little then runs great but if you back off to free wheeling along .runs bad .what do I do

Jets? Your question is kind of lacking in details.

"Won't idle runs like one cld untill you make her pull a little then runs great but if you back off to free wheeling along .runs bad .what do I do " Learning to phrase a question would be most hopeful. We have no idea if this is a lawnmower, car or airplane!! How about helping us out a little more.