Audi A4 1998 1.9TDi keeps going into ECU safe mode?

When your accelerating in 4 or 5th gear from low revs to build up speed over 65 usually it cuts power and it going into safe mode ( Cuts power Stop turbo working i believe) Most of the components on the engine has been changed, i.e Brake vac pipe hoses were changed in audi garage as a recall measure ( problem seems to arisen since then) the air filter has been changed, so has the MAF, and the Boost pressure control valve (Also know as the N75 Valve) just changed the fuel filter as well. Any Idea's?? driving me nuts!!