89 dodge power ram 5.9 (long story)

I know this is forabodies only but there isn't many people on fto. I just got the pickup above and it doesn't idle worth a damn. It lopes and sometimes backfires and then runs fine and continues the cycle. Anything above idle and it runs fine. Nobody knows what is wrong. Replaced spark plugs, wires, rotor cap, fuel filter, egr, pcv, sti, air filter and rotor. This is where it gets expensive and tired of changing parts, need help. Previous owner said that the problem didn't show up on computer.
Only one injector engages at idle. Someone said that they both should and I should switch them to see but they don't interchange. I've heard of similar problems and each one replaced different parts (from injectors to all sensors and computer) and nothing happed. Does anyone else have this problem?