It has been brought to my attention that the OE DV serves two purposes ! 1: DV, 2:throttle controll !!!
When your car (z20let) is at half throttle, you assume the TB butterfly is half open. Wrong its fully open, the oe dv releases pressure. This is controlled by the ecu. Basiclly the OE DV is always working so you cant use the vaccum pipe from the OE DV for anything but the OE DV. And you shouldnt disconnect it.
Any extras like a atmo DV or boost guage must come from the fuel pressure reg vacuum.
I found my car was crap throught the mid range cause the atmo DV was releasing presure. The AMM is telling the ECU theres this amount of air, so the ecu put in this amount of fuel. But the atmo DV is venting the air all the time so you get a far to rich mixture !
Basiclly DO NOT disconnect the OE DV and DO NOT "T" any other vaccum pipes into it !