Ive had the same problem. Lower intake gaskets failed. Amazingly, if you drive sensibly it will run fine for quite a while like that(although not recommended). Make a note though if you change the intake gaskets, change the isolator bolts in the plenum as well, and use a "good" sealant on the gaskets. Do not skimp on it or you will do it again. (i speak from experience). I changed mine at 105,000 miles, 60,000 miles later, and still runs like a champ.