Throttle Problem

[BlueHavenKennel]

I recently purchased a 90 model GT Mustang in which we have spent the past two weeks putting back together. Put the engine back in yesterday and it ran fine until later on this evening. But now the throttle hangs on it. Other than that it runs smooth, no surging or anything. It is fuel injected. You can bump the gas pedal to 2 or 3,000 rpms and it will hang there for 30 seconds to a minute before slowing back down to idle. We are thinking that it may be a vacuum leak but have no idea where to start looking. Any suggestions? I am dying to be able to drive this car but not if the throttle is going to hang wide open on me if you know what I mean. LOL. Thanks in advance.