Do a search for this one and you'll see it's been discussed many times. Usually this is due to a plug or wire, maybe your DIS or even the cam sensor or crank sensor. Best of luck
I also had a cracked sparkplug. By the time I figured that out I had also ruined the new wires that I had just put on. Basically had to change everything again. If it idles fine and you can baby it around just fine then my money is on wires and plugs.