Its a bit of a lottery if you don't have access to VAG-COM.
It could be any number of sensors causing the problem if it is in limp home.
Reset the ECU, and then if is idles [censored] straight away, it could well be a duff coil pack. But you won't know which one.
You could buy just one from Audi and start swapping it around and see how you go.
But to save you time I would get the fault codes read/cleared and then drive it for a bit and then get the codes re-read. This would then tell you exactly where the problem lies.