What function does the black plate on top of the throttle body play? I had a really bad gasket in that spot, so I made one from thin cardboard. Is it imperitive that gasket is exact? Should I get a real one? And the 64 thousand dollar question.... could this be the cause of my idle stumble?

 

air for the pcv system is provided through there. if leaking could effect idle. not so sure it would cause a stumble. i would think it would raise the idle if anything.