so i was cleaning under my hood when i noticed a little rubber nipple on the left side of my head(5.2) near the throttle body i pulled it off and it was so dry rotted it just cracked. underneath was a metal almost looked like a grease fitting on the side of my motor but when running in sucks in air, when i cover it the truck idles down, what is this? where can i get another cover?

 

Welcome to the forum!

Can you post a picture?

You should be able to get a cap at any parts store.

 

just a vacuum line nipple. Keep it capped. uncapped lets extra air get pulled in = more fuel pushed in.