Posting this I have realised that its been well over a year since I last logged in - which means its been well over a year since my Audi gave me any grief! So that is something to celebrate!
Any-hoo. About a week ago, whilst pottering along, my engine warning light came on. I've just now had chance to hook-up Vag-Com and pull the codes - they were:
17544 - Fuel Trim: Bank 1 (Add): System too Lean
P1136 - 001 - Upper Limit Exceeded
16891 - Idle Control System RPM: Higher than Expected.
P0507 - 001 - Upper Limit Exceeded - Intermittent
I cleared the codes and took the car for a 15 min drive and the engine warning light has not come back on. However I have been noticing a slightly 'lumpy' idle recently (which matches the codes) - if I'm stopped at lights for over 20 seconds or so, the idle speed will drop slightly, rocking the car, before (presumably) the engine management picks up the RPM to stop it stalling, it will over-rev for a couple of seconds before settling back down. This repeats every 20 seconds roughly.
Anything to worry about? It's due a service in a couple of months, so I'm tempted just to leave it until then, as there is nothing in the codes that hints at a cause.