Hey, I am having a problem similar to that, must say it not quite the same. I got a 2004 Punto Active Sport 1.2 16v, when i start the car, when it is stationary - whether it is in gear ir neutral, the car is sort of juddering.
This has been happening for a couple of months now but has been getting worse, took it into fiat dealer yesterday and they told me that they had changed the O2 sensor but said i would also need to change the spark plugs and leads - does this sound about right?
Did you change your leads? if so, did it sort the problem?
thnks
kel