That sounds like one of the spacer bushings for the timing belt cover. The dumb covers crack after a while and the bushings can fall into the lower cover when you remove the upper cover.

The worst part of it is, if you're putting the cover BACK on and you don't notice that the bushing falls out into the lower cover, along with that brand new belt you just gave it.

I have done that before on my own car. ANd I'll tell you, when the timing belt broke (with 150 miles on it) because of that dumb bushing, I was somewhere near Cornfield, IL. That little bushing cost me $300 for a new timing belt and a hook. And the belt WAS new.

Don't risk putting that thing back in, if the surrounding plastic from the bushing has disintegrated too much. Just put a washer on the head of the bolt to hold against the plastic of the timing belt cover, or forget the bolt (if it's the center bolt) and put the timing belt sticker over it so that the dust stays out. YOu don't need the small center bolt--the screw and the other two bolts hold the cover just fine.
--
Chris Herbst, in Wisconsin.