5.0 conversion HELP

[5.0BRONCO]

I recently installed a 1988 5.0 into a 1975 Bronco. The engine ran excellent in the car. After making all of the wiring modifications and the balancing swaps it fired. It continues to run good, however it acts like it has a huge vacuum leak. One second it wil idle great, the next it will miss and stutter like it has an ignition problem. I can't find a vacuum leak anywhere and it is too inconsistant to make me belive that it has one. I'm kinda stumped. It runs great at higher rpms, but it tries to fall on its face and stutter when I put it into gear at idle. Is there a sensor that will make it act like this. I had to use the MAP system until I find a MAF computer. Will a bad MAP make it run irratic? Any help is good help. As far as modifications, the EGR has been removed, the sensor in the cooling lines was moved to the back of the intake, the cooling lines going through the throttlebody were removed, and thats about it. Please help