My 99 A6 2.8L has a variable length intake manifold, however the vacuum pod/ lever don't seem to ever move. They are always in the no-vacuum position. It moves freely by hand, and when I connect the vacuum line to a hose with suction, the manifold lever moves all the way. There is a little control valve that has an electical connector plugged in. I cleaned the contacts but didn't see any change. Does anyone know when it is supposed to be in the vacuum applied position (idle, revved up, ...)? Also, can I apply 12v to the electric control valve to see if it is working? I've included two pictures. The first one shows the lever which is just below the coils. The second shows the control valve. I searched some and found some info on other models, but not much on the 2.8 V6. For the 4.2 V8 appears that they are supposed to be fully on at idle.

 

Don't quote me but I think the switch over point from short run to long run is above 5500 rpm.