sounds like a coil pack, ht lead, or spark plug to me, the way to narrow it down is pull off the ht leads one at a time and see if the problem gets worse, if it does you need to check if there is a spark at each point between the 3, so coil to HT, if theres no spark its almost certainly the lead or coil, if theres a spark at the end of the ht lead that goes on the spark plug then id say its the plug, you can check for a spark by offering a ground point for the coil/lead using a piece of wire/similar, watch you ont get a shock though!
if the car is only doing it under acceleration though this wont work.
im no mechanic but have had a coil pack then 6 months later an HT lead go, and the above identified the problem both times
