Wheres the fault on my Corsa easytronic?

I have a Y (2001) Easytronic. A few days ago it started driving jerkily, as though it was running on kangaroo petrol. The problem seemed to be confined to the lower gears, ie setting off and pulling away at junctions, and OK when up into 3rd and above. It also "seemed" a little better when used in manual mode. Today however I drove to work in manual mode and the problem persisted even at around 40mph in 4th and 5th albeit very mild. Its as if its misfiring, but standing, the engine sounds fine both idling and revving.