2.0 HDi misfire/rough idle

[maxxo]

I have a 2.0 HDi xsara picasso

only on cold starts does it idle quite unevenly, if i just touch the throttle to increase revs slightly it becomes a full on misfire and kicks out a fair amount of smoke

however if i rev it slightly more it smoothens out and idles beautifully, only ever does this on a cold start, runs beautifully all subsequent starts

i'm starting to feel this is some form on injection issue

any advice is much appreciated

car has 111,500 miles on it