Here go’s

I have a focus 1.8TDCI 2003 and I am having problems with start up and loss of power. What happens is the car starts fine from cold and runs perfectly normal, goes for a good long run and the engine gets up to temp. Then if I where to stop at a shop say and come back to the car and restart it, it would fire up but only just and ticking over very low. If I where to press the accelerator pedal I would get no revs on the car the engine is just ticking over very low. If I take the clutch to the biting point and just manage to rock the car back and forth the revs will increase and the accelerator pedal will put revs on again but this can take upto 10 mins then when I then set off the car is ploughing white smoke out for a while and doesn’t seem to have anywhere near as much power as it should.
Leave the car over night start it the next day from cold and it’s fine.
It has just been serviced by myself new oil, air filter, fuel filter cam sensor with upgraded wiring and new crank sensor. The crank sensor was fitted by just taking out the old one and replacing with the new. Should I have set top dead centre?
Any info would be greatly appreciated.

Scott