Volvo: 960 Engine Miss, miss ray, rubber boots

Question
Ray, I have a '94 960 wagon whose engine died. It was replaced (500 miles away) with an engine from a '96 960 with about 70,000 miles on it. The "new"engine has been in for a couple months but there seems to be an slight miss and the idle is not steady and moves around, and always kicks up when in park. My local mechanic changed the wire harnesses connecting the coil packs, which were crumbling, checked the plugs, and replaced the seals on the fuel injectors (one was leaking) but he can't fix the problem. Is this engine compatible with a '94? Any other ideas? Otherwise it drives fine except for the rough idle.

Answer
Chris,
If you used the cars original intake and exhaust manifolds, injectors and sensors it will work. The 94 and 96 have fuel system that used different injectors and sensors. I have seen many intake manifolds leak at the gaskets or rubber boots between the manifold halves. You might have a weak injector, one not spraying well. Did you take a compression test and cylinder leakage test of the engine you put in? Maybe it has a weak cylinder. Can this miss be narrowed to a specific cylinder?