94ex_b18b1

Hey guys I just purchased a b18b1 swapped 94ex coupe. i was checking it out and i noticed from a cold start it idles around 2k rpms. the vaccums seem to be good. there is a sensor on top of the intake manifold that has a spot for a vaccum line but there is nothing plugged up there? it idles fine after about 10 mins... i cant figure out what sensor plugs up here or where to find it. is it safe to leave it off? if anone can help it would be greatlyappreciated.