Intermittent misfire Pug 206cc 2002 (1.6 petrol)?

Hi, not all the time, but mostly when its raining or been raining when i start from cold in the morning, i get a misfire. when idleing the car feels like its being shaken. this normally disappears after a mile or two. only every continued to misfire once, after restarting on my way home from work.

I get no warning lights, but do get an anit-pollutant message followed by the cat converter prob.

thought it might be crap in the injectors, the cam sensor or the coil pack...any ideas?