i dont remember anything going there, the oil just drips from either the lower gasket or upper manifold bolts and flows down that way.

William, you're right. That'* the one I'm talking about. I can't figure out what goes there. May have to go to a JY to look at another one.

Although the car is a 99 Grand Prix, I found "97 EightyEight" written on top of the plentum in yellow junkyard paint so the motor is probably a junkyard replacement. I've run into some other issues like transmission vac line that wasn't needed on the GP that I had to plug so this may be something particular to the 88. I'm at the point of just plugging it but I don't want to cause any more problems than it already has.

Thanks guys for all your help so far.

well come to think about it, its the side engine mount on a h-body, which you would not have on a w, they have dog-bone mounts. not likely any reason to care. like we said its just a gathering point for oil from above

No worries Mike, at lest you did not forget you could change thread titles.



Sounds like this car already had somebody attempt to fix the UIM(plenum) I am betting whoever sold the car tried to fix the a leak that they thought was only the UIM, and did not know enough to get the aluminum framed LIM Gasket, and replace it also.
The plenums are the same though.
Like Justin said, no need to plug that hole, the oil is just leaking downwards, and collecting in that hole, no harm can come from not putting a bolt in it..






I knew somebody would be able to figure it out, nice job Justin.
+1

Thanks guys, really appreciate the help. It had me stumped, especially when I stuck an ink pen in the hole and went all the way in without hitting anything. Looks like we'll be replacing UIM/LIM gaskets, crankshaft sensor and a whole lot of other things if we keep it.

Thanks again.