92 Eclipse GS broken?

My friend owns a 1992 Eclipse GS, the SOHC version that he got for 800 dollars. The paint is horrible ,the seats are stained and it's got 120,000 miles on it, but the carpet is alright :p. Anyway when he first got the car it acted like it was running on 3 cylinders, it would shake and had no power. Shop said he needed a new ECU so we get one from the junkyard and hook it up, runs great now no shaking and gets decent gas. But now it's time for smog and we have an issue, the idle. For some reason, unlike most cars which idle at 1,500rpm when cold and 750 or so when warm, his does the opposite. When cold his Idle is at 720 and when it's warmed up it goes UP! to 1,500!!...that won't pass, I'm thinking it has something to do with the IACV, is the IAC motor hooked up backwards or what?? Need some help thanks guys.

Well Mitsubishi IACs are crap and often can go bad. If you can test it then do that, else go ahead and spring for another one. Either that or the ECUs mixed up somehow. If the IAC does its job properly, just kinda backwards then I would think it's probably not the cause.