My shop manual makes no mention of the idler studs. Here is what I would do:
-Chase the two studs holes with a tap.
-Spray the stud holes with brake cleaner.
-Blow the holes dry with compressed air.
-Put one or two drops of medium strength Loctite on the stud threads.
-Tighten as best you can
You need to clean all the debris the stud holes, especially if the original studs were secured with Loctite. I tend to use Blue medium strength on almost all of the fasteners. It hold very well, yet can be broken with a wrench or screwdriver. Fasteners secured with High Strength Red usually have to be heated with a propane torch before removing.