1998 5.7 intake problems

i have a 98 chevy 1500 5.7L, and changed the intake gaskets that started leaking anitfreeze. after going back together with new upper and lower gasket sets, the cpi ( central port injector ) plug that comes up through the center of upper intake will not seal off. the o-ring on the the cpi is new ( felpro / dont recall part # ). i sucks a lot of air in and wants to run as if timing is off, and tries to die when u come to a stop with it in gear. how can i get the new gasket to seal off without breaking anything ( all plastic top half of intake ). i talked to a chevy dealer service tech and he said to use the old o-ring if it was not tore up. i have had this thing apart 4 times 3 new gaskets and now the old one and none of them will seal off ( seals in front but not in back closest to the firewall ). thanks to anyone who can help me on this one.

Sorry, I have not seen this problem. Have you tried using the old o-ring as the tech recommended? Can you by one separate from gm? When you pulled the distributor did you mark the distributor and where the rotor was pointing? How do you know that it is sucking air, did you spray the area with carb cleaner?

BTW, part of the reason that no one replyed to your post is because you are posting in silverado and need to be posting in C/K forum. Just to let you know.