The mass air flow sensor on a Volvo 850 is mounted inline with the intake tubing. It takes a reading of the air passing through the intake tube, and transmits that information to the vehicle's computer. In turn, the computer controls the amount of fuel going into the engine, producing a perfect air to fuel ratio. When this sensor goes out, the computer has no basis to control the fuel, and the car may run rough. Fixing the problem means replacing the sensor.
Pop the hood. Locate the air filter box located on top of the fender well. Locate the electrical harness running into the intake tube. Unplug this harness using your hands.
Unscrew the mass air flow sensor from the intake tubing using a torx-head driver.
Set the replacement mass air flow sensor into the intake tubing. Screw it in place using the factory screws and the torx-head driver. Plug the wiring harness into the sensor.
