Aye, a vacuum leak also can be the cause. That's another thing that sucks. lol Sometimes the leak is sooo small. but enough to cause problems. My old 292 had some leaks...idle RPMs fluctuated like crazy...and sometimes they were fine. Lot of times the valve adjustments fixed those issues. But for an old goat That was a great running inline 6. Just to bad she was worn out so bad. But it gave a good excuse to hop another one up!
