Here's a question for you guys still running the stock emissions stuff.

I've been working on some videos for how to setup/adjust the throttle and idle stuff on a mostly stock S5 TII. This also includes an overview of the stock vacuum system. However, I don't have the air pump, acv, or any of that equipment on the car, and haven't for many years. If I still had it, knowing what I know now, I'd put it back on. That aside, I'm trying to figure out how the air flows through one of the vacuum lines to the throttle body. I have it highlighted in yellow in the picture here.



What I'm curious about is how this vacuum circuit operates under idle conditions. Is this circuit drawing air from the ACV area and into the throttle body under idle/low load? Is this line under any kind of pressure from the air pump that I would need to replicate, or could I just reroute the hi-pressure side to the back of the intercooler and use pre-throttle air? Right now it's capped off, and has been so for many years.

I'm also wondering what the air routing looks like through the ACV if somebody has one lying around and can take some pictures. I've been through the manual, and it shows a general routing of the device, but not overlaid on an actual picture of the device. Thanks a bunch guys

 

so the ACV's have two big vacuum plungers, and these direct the air pump air to where it needs to go. they are in series so one is in front of the other. the Relief switches between Reliving the air to atmosphere or into the second valve. the Switching valve Switches the air between "Port Air" and "Split Air". on the NA cars the ACV is in relief until you apply vacuum to the valves, the turbo i think is in port air, and it uses a pressure from the air pump to move one of the valves (you can see the hose in the pic) and vacuum for the other one. i don't remember which is which, the vacuum rack kind of routes everything for you.

 

So there isn't any appreciable crossflow through the switching solenoid? Ok, so my next question is that there are two small ports drilled from the ACV into the primary intake runners. Since those are now blocked off, but were originally intended to flow some sort of exhaust/pump air mixture into the primary runner, I should need to replace that with an air bleed of some kind right? I'm thinking of bypassing the #1 solenoid, using the top port on the front of the TB as the inlet, and hooking the other end of the rats nest into the back of the intercooler. Not sure how it would affect stuff yet, but it would restore some of the expected airflow to the primary intake path I'm thinking.