alright, i just got a new engine put in my car cuz i blew a piston ..but the new engines got 78k miles on it, and i got it back...and when i start out its like boggin down real bad and buckin horribly..ill give it some gas, wont even make a sound then all of a sudden take off, and stop again..also when i start the car the idle is goin from normal for about the first 15 seconds, then starts goin down to almost nothin and sounds like its gonna shut off, then revs up and does it over again..anybody have any ideas on whats goin on with it?

I'm going to venture to guess the IAC is dirty or something and needs cleaned. You might also check that the vac lines are all installed right too. A lot of idle problems are caused by these guys.