Using a Bosch Mass Air Flow sensor with an ECU programmed for a Pierburg MAF
The schematic is shown here. It basically is a low gain amplifier that also does some level shifting. In the interesting air flow range from idle to full power (50kg/hour to 400kg/hour) the conversion is very accurate. This circuit was tested, but only on the lab table. As the conversion is very good too, there's no reason to suspect that this circuit will not work.