I was initially told my problem was a vacuum leak and indeed I found a small leak hole from one of the hoses from valve cover connecting to PCV split.

When when I replaced the plastic grommet, a deep missed persisted in one of the cylinders. So I pull all four plugs of my Chevy Cavalier 1988 RS 2.0L; three were clean (like grayish brown ash on plug's tip) but #2 was distinctively different, i.e., caked with black carbon.

It was suggested to me to check/clean the #2 fuel injector; but I don't know. Can anyone suggest the next right component to check. (Should I do a compression test of this cylinder?)

Thanks, Chevy Crew