i have a 91 accord i bought with a bad engine...i pulled the engine out of my 92 that was totalled out and installed it in my 91...i got it running after changing ecu's etc...anyway when it fired up it revvs up and down...i did some research and found out where the map sensor was which was in the control box...i changed the control box and the car still does it...any advice?

 

At idle, is it bouncing from 1-2k? Had the same problem when I got my car off my brother. Try bleeding the coolant if you haven't already.

 

A few things can cause that.

Air pockets in the cooling system like a.newhouse says.
Vacuum leaks
Bad, sticky IACV
Loose plunger inside the FITV
Improper adjustment of the boost valve on the other end of the intake manifold.