1995 3.1 monte idles rough

I just did a motor swap thanks to blown head gasket and now the newer engine idles rough while in park and while accelerating.Its a 1995 Monte Carlo ls 3100 with 64000 on engine 162000 on body. I used the better of the 2 motor mounts and most of the original parts. It acts like its got a major vacuum leak or fuel problem. But both seem fine. Any ideas? Please let me know

Did you use the injectors from the old engine? You may have a stuck/bad one. Give em all a tap tap with the engine running and see if they pop loose. Can you hear a vacuum leak or anything?

Yes used old injectors and no vacuum leaks running rich tho. I pulled plugs and they were wet and black i changed them runs a lil better but gonna seafoam it to see if it helps

just a nudge. I got the same thing going with a 3.4 DOHC. injectors are good but can't hold fuel presure. Thinking that the fuel pump might be bad.

So you originally had '95 monte with a 3100 and you put a donor 3100 from what year and model? Are you using your original PCM? I think most of the '95 model years had the obd1.5 with an electronically flashable prom. You wouldn't think so but even if you got the same engine from the same year and model it might not run right without being reflashed. On pre-95's you could just switch out the prom from the new engine's ECM and you could also unhook the battery and the ECM would reset itself. This is not the case with 95-up. It might trim the fuel curve over time itself though. Does it run rough even when it's fully warmed up? And no check engine lights right?

Other than that the only thing else I could suggest is to check fuel pressure and make sure it's not too high (bad fuel pressure regulator) and check the ignition wire resistance and coil secondary resistance. You could also check each injector's resistance at the fuel injector main connector. Without a scanner you can't really check TPS, ECT and IAT values, which are other things I'd look at, but if these are off much they normally set a code anyway.