Misfire??

[fastbikerr1]

I recently bought a 97 reg A4 avante with 100,000 miles on the clock. It has been regularly serviced. The battery was completely flat though it started fine from a jump start. It drove fine for about 80 or so miles till i parked it up that night. Next morning it started fine and ran like new for approx 10/15 minutes. Then for some reason it started to run really lumpy with a loss of power. It still drove pretty well and every now and again felt as though it wanted to pick up again?? It was parked up all day while i was at work and i had a similar experience that evening?? Now when ever its parked for a longish period ie. over night its fine foe the first 10/15 mins or so. Apart from this it idles fine and quietly until after the initial 10/15 mins?? Any ideas?? It has been suggested that the automatic choke is stuck on??