Mas air flow sensor problems on a ford fiesta 1.4 tdci mk6?

I installed a new mas air flow sensor on a ford fiesta 1.4 tdci mk6 but it's really down on power. The sensor is a bolk one that I got of the Internet. Can anyone help

Hi surprise surprise it needs mapping into the engine management computers system.
you just can't change it that is why a dealer charges so much to fit it.

What made you think the MAF sensor was bad in the first place? Did you test the voltages? Buying a MAF sensor on line is a joke. Get one from the dealer using the VIN so you know it's the correct MAF for the vehicle.