twentysevenlitres

An engine stalling when slowing down for lights or intersections etc is often an issue with the speed sensor or crank angle sensor.

Used to happen to my old man's Pug 306 with the 1.8 8V PSA engine whenever it was in closed loop (that's every light, every intersection - drove us crazy!) until we replaced the speed sensor.

The 12V V6 fitted to early A4's and A6's had an inherent software glitch that would cause those very symptoms on very hot days (wouldn't happen to me until the temperature exceeded 40 degrees C) when for some reason the fueling wouldn't catch in time from a no fuel condition (off throttle slowing down) to idle required (probably vapour issue with hot weather, needed more fuel initially).
Apparently it was fixed with a software patch, but Audi knew nothing of it when I enquired.
Never heard of any similar issue with the 30V's though. And England isn't exactly known for its extremely hot weather ;-)