Manual trans.94 toyota pickup sputtering only in idle.?

in idle the engine revs up slightly and then sputters down to regular idle speed and then up again. It is doing this over and over in about two second intervals. If I put it in gear and slowly engage the clutch to move forward or back slowly, it stops the sputtering. Once moving in gear everything is normal, but the moment you take it out of gear and go to idle it starts sputtering again. I first thought maybe fuel filter but I had a car with that problem before and it sputtered in gear and out. So I dont't think that is it. Any ideas.