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If it is standing still and is suddenly idling rough, that is not referred to as shudder. A rough idle can be a bad plug, a plug wire, a valve, a lifter, a valve spring and any of which can be diagnosed by a mechanic and corrected.
The "shudder" problem, discussed on this forum, is a transmission problem that happens on the A8. It causes RPM fluctuations and surging while driving down the highway. This situation is also in need of a mechanic for a triple flush and some software update.
So, bottom line, see a mechanic to get your idle issue corrected. As long as it is doing it all of the time, they can fix it. If it is sporadic, then it might be a challenge to correct.
I agree with Elmer it isn't a TC shudder issue if it does it sitting still. You have a bad pulg, plug wire or coil pack issue. Take it in and have it fixed.