Missfiring when cold!!!!

Help.

I've just carried loads of 'repairs' on my defender and have developed a problem - well loads of problems - i have search the threads and resolved all but one which is now beyond me.

In a nutshell it was very poorly (cracked head) and as a result it has had a reconditioned head, which i have fitted. I have done everything Mr Haynes suggests but when starting from cold it only runs on 3 cylinders, but after driving for about a mile or so (once warm) it is sweet as nut.

Any ideas why it would do that? I am praying its not a compression issue in the cylinder offending cylinder!

I've just realised the thread is not where i meant it to go and you won't know what engine it is. it's a 300TDi. soz.