Carb ecu is at open loop at idle, and the idle is normally rich, just like Kevin said. I took the SAS off my turbo so long ago I don't remember how that one worked. I chopped the pipe, crimped it flat, and welded up the end, about 2" from the gland nut on the turbo exit housing/downpipe. It's just after the ohtwo sensor, of course...

Never had to pass smog with it, either. Registered it at an accomodation address in a non-inspection county, and I live in that county now.

I ran the turbo D50 for years on just the downpipe, stopping at the cat flange, and can tell you the 2.6t also idles rich, based on the smell. I read somewhere once that the rich idle had a beneficial effect on turbo spool up, because the unburned fuel in the exhaust stream between the port and the turbo lights off on snap wot and adds a pop of energy to the exhaust stream as the turbine accelerates. Sort of a poor man's racing Porsche exhaust flamethrower effect