[V8] Engine Still Not Running Smoothly ...

[Jason Wilkerson]

The short stubby hose for the breather system is on the drivers side right behind the ISV (actually to the right of it as viewed from the bumper)  It could cause the sound, it could be cracked in the back and you never see it.  You may try spraying WD-40 or the like in the area and see if the idle changes?  Those hoses (there are two others just like it) are known to deteriorate.  Fourtunatly our engines aren't full of vacuum lines like other audis of the same period.  Good luck.