Aussie

My 4.2Q occasionally (now more frequent) runs quite rough just after you start, both hot and cold. Feels like a bad plug. After say two blocks driving and/or a couple of minutes it goes back to a perfect idle and will stay that way until you start again.
Occasionally the red "cat" (catalytic converter) light comes on and then goes.
Any suggestions or change the plugs straight away?

Egil A64.2s - S6

I don't know why, but it seems like the back plugs go first, possibly heat related or just because they are the most difficult to change?

I had a similar problem with my '99 A8 and the back driver side plug was replaced by the dealer. It fixed the problem.