Inside the air box is a sensor (it is controlled by outside air temp), that opens and closes to allow vacuum to pass from one line to the other. I believe on my 86 2.9, it controlled the EGR in some way.
White 2002 Ranger XLT Extended Cab 4.0 4x4 4.10 LS
K&N CAI 77-2529KP
2 1/4" Exhaust
Explorer Dome Light
IN THE WORKS:
Sable Electric Fan
“If you do not know where you are going, every road will get you nowhere.”