I have a 94 Deville Concours with a Northstar Engine. It has a problem no one can figure out. I was first told that the problem was a faulty manifold gasket but that was not the problem. I have replaced the computer and things got a bit better but it still runs very rough. I checked the map sensor and it showed an open so I replaced it and it got worse. The map sensor connection is good. Any clues as to what to look for next would be greatly appreciated.
Phil

 

Insulation on wires in wiring harness to intake manifold tends to deteriorate causing multiple shorts. Look between manifold and connector near transmission. Sometimes breaks in insulation can taped up. Harness maybe available new, but it will be pricey. Codes? Also check ground wire on right side of engine near right half shaft.