Problems with a 94

Have you changed the plugs, wires, and pcv valve?

check the oil for a white milkyness color. check the coolant for an oily film. i am willing to bet that the problem is the head gaskets and that will definately cause the missing at idle and while revved plus the smoke. i had a 71 swb f100 with a 300 I6 and the fan belt broke without a smell or noise so it overheated and blew the head gasket. it ran like total crap with a big cloud of white steamy smoke. i looked like a freight train. anyways while accelerating it would be missing extremely bad and then all of a sudden start running good for 1-2 seconds and then back to missing. do a compression test first thing after looking at the fluids