A car's engine uses an air intake in order to retrieve air from outside of the vehicle. The air is then mixed with the fuel, and combustion is the result. This is what propels the car. There is a sensor on the air intake called the mass air flow sensor. This sensor calculates how much air to mix with the fuel. If you are using a cold air intake, the MAF sensor might not be calculating properly. This means you are not getting the added gas mileage that most cold air intakes advertise. You can bypass the MAF sensor, and allow the O2 sensor to calculate how much air is needed.
Turn off the ignition of your vehicle and open its hood.
Disconnect the negative battery cable (red). Locate the mass air flow (MAF) sensor on the air intake.
Grasp the wire harness that connects the MAF sensor to the power unit in the engine compartment and gently pull it out of the MAF sensor. This will disconnect it.
Reconnect the negative battery cable to the battery and close the vehicle's bonnet. When you start up your vehicle now, the vehicle's computer will not look to the MAF sensor to check air to fuel ratio, but will bypass it and go to the O2 sensor to calculate the amount of fuel to mix with the air.