4runner vacuum hose

I found a vacuum hose that runs from the drivers side to passenger side
in the back of the engine was disconnected in my truck. On the drivers
side it is hooked up to s "speed control" unit just inside of the
fender near the windshield and it is disconnected on the passenger
side. I have looked through all of the vacuum hose diagrams I can find
but I don't see it listed anywhere. Anybody know where this hose is
supposed to hook up?