hi a new in the forum

so i have skoda octavia 1.9 tdi 90 hp 2002
the problem started a year ago . the mass air flow has stop working
that what the mechanic say, so we replace the sensor (the orginal VW sensor) and the car go wild for 5 days the power was more than he was befor the old sensor faild
after 5 days the car return to the point befor the old sensor faild
i replac the sensor another time with new one. the same thing a few days of power and the car return like what she was befor

so the mechanic chick with that thing computer and says the new sensor is fine
so what the problem
thank you