Thought that I would give you all an update with the problem I experienced with my new (10 days old when taken back to dealer) s4 cab tip. Thanks for all the replies. Decided that rejecting the car is not the best plan, certainly at this stage, as I could get my money back but I'd be stuck without a beautiful s4 cabriolet for at least 3 months and as I have a good relationship with the dealer and it's not their fault. They have given me the one and only s4 cab demo they are currently running, which is nice (and an s8 3.7 for a couple of days so that they could use the demo for a previously booked test-drive). The car's replacement gearbox is due to be fitted on Monday 24th May, having taken 10 working days to arrive (due for delivery to the dealer on Friday 21st May). It's comforting that nobody else has replied to say that they have had the same problem, i.e. revs fluctuating whilst driving at constant throttle or gentle acceleration at between 1000 and 2000 revs. If the problems still exists after I get the car back, or manifests itself again thereafter I shall reject the car, but I thought I'd give them a chance to rectify it first. I will report back next week once I hopefully collect the car.