Engine malfunction

[Bloodyford]

Having problems with 2011 1.4 disel ford fiesta zt where this symbol comes on slight loss of power engine will cut out if engine revs drop below 2000 with a flick of the switch without engaging the starter engine comes back to life but if revs are still below 2000 will cut out again crankshaft sensor changed, fuel filter changed high pressure fuel sensor changed, fuel pump regulator changed running out of options any ideas thanks