In modern cars a "tune up" is usually just replacing things like air filter, change the oil, and change the spark plugs, etc. Days of old, you had distributor, points, etc. etc.
If the plugs have never been done, you are due. I believe it's 70k miles or somewhere around there where they're supposed to be done. If the plugs have 85k miles on them, this could certainly be a source of rough idle (with no CEL).
Personally, I would just put new plugs in it and see what happens.