Vehicles loses power and has flat performance intermittently. 50% of the time runs very well, 50% drives very slowly on acceleration and has a slow top speed. 5 fault codes listed: 18027 Glow Plug Heater Relay Circuit; 17946 Engine Shut-off Solenoid; 17849 EGR Valve Power Stage; 17957 Boost Pressure Control Valve; 17660 Start of Injector Solenoid Circuit.
Have changed Air Mass Meter, Boost Pressure Control Valve and Glow Plug Relay. Drove OK for 10 miles and then engine management light came on and back to original fault. Codes still in memory.
Have also smoke tested intercooler and all pipes with no leaks found. Have checked Turbo for free movement. Have checked all electrical connections with no bad connections found.
Has anyone had a similar problem? Any advice gratefully received.