...bad sensor which caused it(fuel/oxygen).
Can you feel anything through the accelerator pedal? does it feel like the engine is faltering or is the engine feeling/sounding consistant while it makes the 'ruffnous'.
Adrian, I had been thinking this, too. PCV valve, gunky throttle-body, etc.
Randy, when you start noticing the symptoms, can you put it in neutral, rev the engine and see what happens? I had a somewhat similar problem with our Ford Windstar that turned out to be an oxygen sensor. Obviously, if the engine revs freely from idle to redline, that is not the problem, but it might be worth checking.
