missfiring on ford galaxy 1.9 turbo diesel,52 plate?

i have a 1.9 turbo diesel ford galaxy 52 plate, when i start it in the morning it sounds as if it is only running on three cylinders. once it is warmed up i turn the engine off leave it for afew minutes re start it ,it then works ok. if left for a couple of hours i have to repeat this until warmed up again. would appreciate any feedback on what is causing this problem. cheers.