406 hdi misfire/underpowered?

Hi Guys
I have a 2002 406 hdi with siemens fuel system which is starting & running but seems to misfire and hesitate and is underpowered.Have had the car on diagnostics which showed a faulty MAP air sensor (now replaced, new) but is still the same.
There is some air in the fuel pipe from the fuel filter to the injector pump which seems to be worse after revving
it as the throttle is released.I heard the hdi is self bleeding but should there be any air in the pipe at all?

Grateful for your ideas!