Clio 1.2 rough running when cold

Hi, i have just bought a 51 reg clio 1.2 authentique and have noticed that when you start the car up from cold it starts and ticks over lovely and smooth and doesnt miss a beat. After a few minutes the revs drop and it starts running rough. The revs will drop up and down for a couple of minutes then whatever is going on seems to clear itself, the rev counter goes up to about 800 and it runs smooth as anything and carries on with a lovely drive. I noticed this when i was driving and at the same point (just up the road after starting it) the car lost power and i had to pull over to the side of the road until it cleared and then drove with no further issues. Any help would be greatly appreciated. Many Thanks

Clio 1.2 rough running when cold