Rob G60

Hi when cold my g60 runs rough not on all cylinders then when driven in the first minute or so can cut out if accelerated too hard. It makes a slight shudder sound before the engine dies! The engine has a rally cam stage 4 charger 68mm pulley and tsr head but used to run fine. I have ordered some new plugs bosch w6 dpo. If anyone can shed some light on my problem it would be much appreciated.