Upstream exhaust valve
 

Can anyone tell me how the upstream exhaust valve opens & closes or does it work with the rear valve. I have the rear valve open all the time but i can hear the up stream valve opening and closing. I have an A6 Z51 npp exhaust. When the valve is opening and closing sounds like the car is choking.

exhaust
 

I have the same deal. Mine is an auto and it happens under light acceleration around 1700 rpm. Sounds like crap. Someone said pull fuse 41 and it will stop with no check engine light lit.
Don't know what operates it though
Ed:iono:

Yes that valve is connected to the AFM on the car to help with emissions and drone I believe. Only way to get rid of it is turn the AFM off in the tune as even the Corsas you cut after that valve and slip on so they're retained with it too.

The way it was explained to me is that it only operates in Eco & Touring modes for automatics, and only in Eco mode on manuals. In most situations while in those modes, it will default to open, which is to say whenever it is running on all 8 cylinders. They only close when on 4 cylinders, and only intermittently at that. Kind of a computer-controlled flutter to help offset the imbalanced exhaust pulses created by running just 4 cylinders. The valves shouldn't be operating at all in Weather, Sport or Track modes, since AFM is deactivated in those modes.