mk2 vw golf 1.6 driver running rough on start up?

on start up my golf runs really rough (mainly in cold)
have changed air filter,plugs,leads,ditrib cap,rotor arm as seemed to be running on 3 cylinders (yes really that rough ) but as soon as engine warm runs sweet as a sweet thing ?
could my auto choke be shot ?
is it a carb problem ?
help please !!!!!

thanks loads !!!!!!