Pontiac 6000 engine troubles

[automan63]

I have a 1990 model Pontiac 6000 le with 3.1 V6 engine.It has a miss and overall rough and low speed idling ccondition..I have replaced plugs wires and coil packs.Checked for fault codes because check engine light came on but none are showing up except code 12 which is the the normal computer fault code.I was going to change fuel injectors since this engine has 160,000 on it.Im wondering about the planum I have to remove.Are there a gaskets that have to be replaced if removed.I dont know what else to check on this engine,Im at my witts end with it.Help Aaron

[TRDmkII]

well my guess is that there probably is an injector bad, also make sure again that all the coils and wires are going to the right cylinder and that the plugs are gapped correctly. If you are removing the plenum there are gaskets you should replace...what i would do is just go to the parts store and ask for a plenum gasket....goodluck