At last, I have got to the bottom of my running/stalling problem.
With the continued and very much appreciated help from Aragorn, Mark and others I have managed to source the MAF problem, sort the N80 valve fault and it's now running sweet, with no stalling or poor idle.
So... there's no more "Oh God, Giles is asking another stupid question again" to be afraid of anymore!
I'd just like to thank the guys who have given me fantastic advice and support over a LONG period of time to get my A4 working. I am well chuffed and am VERY VERY happy!
Thanks again chaps. You know who you are (all the usual suspects Mark, Lee, Docurly - and particularly Aragorn who's always been there with excellent info on wiring, etc!)... BIG KISSES!