I have a 1994 Mustang with a 3.8 engine. The old engine blew a head gasket and I replaced it with a gm reman engine. The new engine only has 2000 miles on it. Prior to replacing the new engine the check engine light was on. I did a diagnostic check and found that one bank was rich and the other bank was lean. Then the head gasket blew. While replacing the engine I checked all of the vacume lines and replaced any that looked faulty. The new engine has new plugs and wires and the injectors were all serviced by a shop. The check engine light is still on but I have not done a dianostic check yet to make sure that the code is still the same however I believe that it is. The new engine ran great however it sat for one week and now I notice that when I you rev the engine it almost dies and you have to feather the gas to keep it running. Once you feather the gas some then it will rev up. I was going to replace the O2 sensors as they are old and would be wise to replace them anyway but really don't think that will fix my porblem. I was hoping that someone could give me suggestions as to what might be causing the dead spot. I pulled all of the plugs and they are burning clean and correctly.
Thanks Forrest

 

Well the 02 sensors are used during first startup, so that wouldnt fix your problem. Running the codes on it would be the first place to start. Theirs just so many things that could cause your problem its really best to narrow it down as much as possible.