BAC what does it do when disconnected?
 

hi guys!

i have an s4 with microtech, the BAC was SUPPOSED to be removed durring installation of the microtech, but it's still sitting there with the hoses cut.

is this causing a vacuum leak?

I have an 89 GTU and there are two lines, 1 coolant &
1 Vacume. They must have by passes your BAC if your
coolant line is cut. I'd think you have serious issues if
they just cut the lines.

Incorrect.

There two small lines leading to it are coolant feed. One feeds coolant to it, the other takes that coolant away. This same coolant circuit also runs through your thermowax assembly.

There should be a large vacuum line connected to it as well. This is how the BAC works.

Leaving this vacuum line disconnected should not do anything; the solenoid should be closed. However, if it is sticky, or weak, it might not close all the way.

K2RD sells a well priced BAC block-off plate.

****BAC what does it do when disconnected? ****

It sits there quietly wondering why you would disconnect it when it was cycling its damn ass off trying to help you maintain a consistent 750 idle.

There is one large hose coming to it from the intake. That supplies clean filtered air to it so it can inject that air into the intake after the throttle body to make the engine idle faster when the demand is there. There is a small water pipe attached to its side who's only reason for being attached to the bac is to prevent the piston in the bac from freezing/icing up during the winter months. That water pipes primary reason for living is to supply a return path for the water that is returning from the water thermo devivce on the throttle body.

Read this http://www.teamfc3s.org/info/articles/idle.html and the part about the BAC.