So I have my LS1 up and running however, I have this vacuum nipple on the right side of the front part of the intake manifold http://www.ls1truck.com/upload/files/251/IMG_4111.JPG

Its the one on the upper left with the silicon around it. From what I understand Its for the evac system which i think i had eliminated with the tune. If I uncap it the truck runs fine, if I cap it it the truck tends to die out and idles too low to run the ac and also when the truck shifts out of park to rev and drive etc. I know it needs to be either capped or routed to something. Any Ideas?