How can I fix the problem, 1.9TDI?

My car was dioing 70mph and lost power.There was no turbo kicking in at 2500 revs. RAC called out on M11 NO number on TECH2 machine had it serviced and they think its the air valve. Took it to marshall and they could not find any fault on management system. They think its fuel pump poss failing.may need NSI PUMP, INJECTIO REBUI. Please advice what is the best soultion. new pump is £2021+ vat