Peugeot 607 Cold Start Idle Miss/ Hiccup?

[hillkidstr]

This is a weird one that has me confused when the car is cold and is started the engine starts straight away with no smoke but randomly misfires? or hiccups every few seconds after about 2 minutes its gone and for the rest of the day the car never does it, straight away i assumed glow plugs being a diesel so I have replaced all 4 and the glow plug relay I have checked with PP for any faults there is none and also tested that the glow plugs are working which they are. I have checked the injector corrections and all seem ok fuel pressure also seems good (although im not 100% sure on the correct pressure its showing a rock steady 267bar on idle and increase as the revs increase) , this is a very recent thing and it has never done this before the thing is when I went viewing a few of the 2.2HDi's alot of them did the same on a cold start making me wonder am I missing something completely obvious as it must be a common fault? the car is relatively low mileage for its age 70k on a 03 plate. The very interesting thing is that I purchased a 51k mile Citroen C5 the same engine and gearbox and swapped the engine into a different car just before the engine swap the Citroen started to do the same thing but since the engine has been swapped it hasn't done it since so as I have used the fuel pump, injectors and various other parts I am assuming the I can rule these out on the peugeot? But i haven't used all of the sensors from the car I would of assumed that the car would show a fault code if a sensor was down or reading off?

I am open to any suggestions I have been wondering about the fuel pressure regulator but as the Citroen did the same thing and doesn't now and I have used the same pump I would assume its ok?