mine (2002 s4) did that. I desmogged it and was idleing @ 6-700 rpm. I brought it in for warranty work and they bumped it backed up to @ 1100. Don't know if I did it before, that was the first mod I did. Warm up was always the same.
Quite the contrary, after freeway blast to work (about 25 minutes @ 75 mph) I'll notice my idle rises slightly. All smog stuff is still intact. Never seen the low idle. Did you simply remove the smog can or did you use an aftermarket kit such as the TPO? I'm considering installing that kit and am very curious as to others' experiences. Thanks!