Installing Fabspeed Muffler, do I need this
 

I have an all stock 89 930. I am planning to keep it as factory as possible with a few exceptions. I am replacing the muffler and cat with a fabspeed muffler (no cat). Otherwise the car will remain mostly stock. The Fabspeed did not come with the air tube that feeds what I believe to be the diverter valve. Should I add this tube to the fabspeed and hook it all up as is, or start removing the parts?

My stock exhaust system is the lower one in the PET. The tube I am referring to can be seen between parts 17 and 19. It all connects up to the assembly shown in the other parts diagram.

This is what the air tube connects to:
http://forums.pelicanparts.com/uploa...1327267571.jpg

Here you can see my muffler, the lower one with the dreaded cat. Note the tube between 17 and 19.
http://forums.pelicanparts.com/uploa...1327267814.jpg

and the full assemblage of regulation induced HP killers
http://forums.pelicanparts.com/uploa...1327267841.jpg

If you don't have a cat anymore, you don't need to add air to it for further combustion, which would be the purpose of that pipe.
If you don't have to worry about annual smog tests, all the extra air pump injection stuff can go.

No smog here for cars older than 20 years so I am good. So essentially I could pull all the air injection stuff off, completely. Could I also leave it in place to keep it close to factory, and let it inject into thin air by disconnecting the line that feeds the cat? Basically separate the rubber hose (18 above) from the cat tube and then leave it? It would inject air to the street at that point.

If you know for a fact that your air pump is functional, sure. After 20-something years, though, many are not due to belt or pump failures. There's some evidence to suggest removing the air injection ports in the exhaust port if they are not getting air to them. Without air, the thin jets cook unmercifully to red-hot and eventually can begin to erode, sending particulates through the exhaust side of the turbo fan.
They really only help emissions at idle anyway.

OK, thanks for the great advice. Which is if I read you correctly, remove all the air injection stuff and get it out of there.

Robt when I installed my exhaust I ended up gutting the entire smog system. There are plenty of threads on it if you do a search. Search smog system or air pump system or pollution system delete and you will find good directions.