Engine High idle 2500RPM please respond asap

could be the IAC... you can clean it and see if that helps... but, i think you've got a bad TPS...... they are not very expensive on a mustang...try clearing your code.... if the code comes right back, you've got a "hard" code, meaning it's a broken Tps... try unplugging the tps and see if there is a change in the idle... also... you might want to check all you're hoses and see if you have a vacuum leak... fords are notorious... replace anything that looks rotten.... also, sometimes, you can't see a crack in a hose unless you take it lose... i had an explorer with a hole in the hose and you could not see it, because it was on the back side of the hose.... i still vote for a new tps... probably around 40 bucks or so.....

leaning to vacuum, I'd try the starting fluid around hose connections and see if engine speeds up, showing a leak location. real cheap test and fast way to verify

sounds like choke issue, maybe if after start, still cold, you unhook the automatic choke and see-