Mass Flow Sensors?

I have a problem with my 1999 1.8 Nissan Primera P11 in that after about eight or nine miles it refuses to accelerate. It seems as though the brakes have been gently applied. Indeed, knocking it out of gear seems to confirm this. I have been advised that it could be a problem with the mass flow or temperatue sensors. What does a mass flow sensor do and how can I check that it is working correctly?