Unknown Threaded Hole in Engine Bay
 

I was working on some other stuff on my 99 XJ the other day and noticed this hole just behind the TPS, looks like it should have a bolt or something in it, anybody have a clue what belongs here/should I fix this?

https://cimg7.ibsrv.net/gimg/www.che...680ac1fc56.jpg

(hole in question is near the middle right of this picture)

That is an empty spot on mine also. 1999 intake on 1996 XJ.