tough problem to solve

I have a 2002 Ranger 4cyl with 90k miles on it. Ever since it was new this thing has on occassion run REALLY poorly. It will smoke out the tailpipe, barely idle (even with throttle) and miss really bad. It only does this once every few months now. The problem was a little more frequent when it was newer. Initially, the problem seemed to happen only after filling up with gas, but now there is no connection. The problem disappears if you turn the ignition off (I'm not sure about sitting/cooling off time) The dealer has checked it out without any luck (no codes). It drives daily without any other problems.

i use to have a saturn that would do the same thing. i would try a new distributer cap and plug wires as well as plugs. this is the cheapest way to start trust me. then go on to the fuel pump and filter. if not that then i guees it gets really expensive, cause you'll need a new engine.

You may want to try the idle air control valve. It should be bolted on the intake.