vacuum t-piece

Hi,all RR-92 i have one question:I have a broken vacuum t-piece(behind dizzy) It is blocked from tee and also blocked line from plenum!Does anyone know purpose of that system??Sorry about bad explenation,hope some one understand what i mean?I have quite low idle speed and i really want to solve this problem.I know that i should first check ignition timing and then try to adjust idle speed but i have imagination that this vacuum t-piece have something to do with idle??I have cleaned stepper motor. Help required. Rgds:Jukka RR-92 3.9 with cats PS:I have tried to adjust idle from throttle boby by 1/4 turning screw but nothing happened so turned screw back to bottom!