My 96 had a bad valve that was causing a misfire and threw a p0305 so I got a new valve for the 5th cylinder. I seated it and everything. I put everything back together with new gaskets and I replaced the old injectors since I had the intake off. Now that everything is back together I’m getting a p0171 code. The truck idles rough and if I’m out it in gear it doesn’t go anywhere without dying. When I give it gas it sounds like it’s going to stall but once I get the rpm’s up it sounds fine. Hooked up a smoke machine to it and found nothing. I’m really lost if anybody has a idea of what’s going on and can help I would appreciate it.

Also if I push the gas pedal down far in park or neutral it sounds like it it’s backfiring through the intake

 

Verify proper fuel pressure.

Put the original injectors back on. There was no reason to replace them and you did not have a lean issue before replacing them. Were the new ones oem?

 

Generically, P0171 means air-to-fuel ratio of your vehicle is too lean. Along with fuel pressure, also check your IAC, and TPS and MAPS sensors, and the EGR valve/sensor, all of which relate to air inotake and influence the ECM for air/fuel mixture in one way or another. Get replacement/test units from a u-pull-it yard instead of buying new Chinese versions..

Also ensure you've routed your spark plug cables properly. Backfiring could be a plug firing out of order.