2500 van engine problem

ok...kinda hard to explain but i will do my best. its a 88 GMC Vandura 2500 with the 350 TBI engine. One winter when we were drivin it it decided to race the engine so it would idle at probably 2500 rpm and wouldnt go down, but then it did settle down and now at idle it will idle really low and then high and then low over and over. It does this more when the engine is cold but it does it a little when warm too. when you try to rev it up in park it will just spit and sputter and wont rev up, same with tryin to drive it, its a joke because there will be no power whatsoever and it will jerk and sputter. Sometimes it will also die when you put it in gear. I replaced plugs, wires, cap and rotor, knock sensor, ignition coil, oxygen sensor, EGR valve and temp sensor. none of those helped. what should i do next???? what could the problem be...timing maybe???

I'd check the fuel pressure and confirm good fuel flow, also make sure both injectors are spraying.

My friend had the same problem with yours and he found out he has poor fuel flow and his GM fuel injector not spraying properly... Maybe you could check it...
(http://www.dubautoparts.com/volkswagen-fox-parts.html)