Engine intermittently sputters/runs rough while driving and idling. Changing RPM will temporarily fix/change the issue. Seems to happen the most around 2000RPM. This vehicle was just given to us so I don't know a lot about it. I've picked up a fuel filter and I believe I hear a vacuum leak in the engine but haven't pinpointed it yet. I'm unsure if this could also be related to timing and not just a possible fuel or vacuum issue. Any clues on what to look for would be greatly appreciated.