330cd diesel coupe poor fuel economy

hi, i have a 330cd diesel 204 bhp coupe, i am only averageing 29 mpg and that is driving very carefully on country roads, if driven normally about 26 mpg, car runs fine no rattles black smoke or anything, it has new air, fuel and breather filters fitted, no fault codes either, iv tried a new air flow meter and map sensor and still no joy. any ideas would be appreciated. i had a 530 diesel a couple of years ago and averaged 45 mpg with it so bit dissapointed with this car now.

Wow, that's bad mileage. We Yanks don't have that model, but there can only be two things: no air or no fuel. No air means check turbos, wastegate, intercooler or manifold. Fuel means injectors and pump. Does that model have a DPF? might be clogged

this one does not have a dpf it has a cat but iv taken that out so its straight through, iv tried a set of injectors, it has a new turbo with electronic actuator and no fault codes, iv remapped it and it goes like a rocked and its made it better on fuel it only used to be about 27 mpg

i did a steady 40 mile trip keeping about 60 ish and it came out with 36.9mpg not great.