Thanks for the replies. I have already cleaned the throttle housing and idle control valve. The emissions are fine even when it is acting up. It can stall when stopped also but you have to encourage it by going full lock on the steering as the revs are dropping. It behaves exactly the same way VW's do when they need a throttle body clean and reset. The only difference is it only happens sometimes, mostly behaving itself.
Got a dealer to do an ECU update.
Seems to be OK now.
Thanks Fiachra.