My 93 Subaru Legacy sedan, non-turbo, 5-speed manual tranny, 192000 mi, will intermittently stutter at any speed in any gear. Think about driving to a stop sign in a higher gear and forgetting to push in on the clutch. When it starts to buck? That's the feeling it gives briefly while driving at speed. It only lasts maybe 1 second. It may happen several times in 5 minutes or not at all for an hour or more on the highway. May happen going uphill, level, downhill. It also happens in town at 20-35 mph. Otherwise, it runs great. Starts right away. Good fuel mileage. No codes. New fuel and air filters. Clutch works well, not very old. I tried turning the key off and on while driving. It begins to slow with the key off until it resumes running with the key back on. It is not rough (doesn't buck) in that test so I don't think it is ignition failure.