I know how you feel mine is not as serious as yours and im pulling me hair out.I reckon Once you find were air is getting in you will sort it ,took mine to a different guy today. he checked the fuel pressure and it still is bouncing all over , Wonder if anyone out there as had this problem.had 3 injectors replaced on it a little better but still not right.its only still doing around 22-23 mpg AT BEST .
I still have some warranty left 5 - 6 weeks going to see te dealer see what he has to say ,his engineer as given up now.
the trouble is i have friends who have the same td5 gs same year and return a better mpg then mine with more milage on the clock 85k and 129 k,mine 48 k.
will let you know if i find out what is causing the fuel surging.