Vauxhall Vivaro idle mode

my vivaro started going into idle mode when i put my foot down engine management light came on and it would cut out.put a new fuel filter on ,that didnt work.put onto a diagnostics machine showed two faults injector and pump both have been replaced and its still doing it ,the diesel specialist garage dont have a clue they have tried all these solutions ,checked the fuel lines there ok ,ecu unit is fine ,wiring lomb is good.they say its still doing it.....i feel it was a simple problem and the garage has kept hold of my van to try and deflect from the unnessacary expensive work they have carried out ...please help im self employed and being without my money earner for 3 weeks is crippling me