Check the wiring. Go over the steps you took putting the intake on and see if anything's up with the MAP sensor. That's not a sensor you just want to have messed up. The MAP sensor is what reports to the ECU regarding your the pressure inside your intake as opposed to the pressure outside. The ECU reacts to this sensor by updating fuel/timing maps. If the MAP sensor isn't reading correctly, your ECU isn't dynamically tuning the engine correctly resulting in poor performance and gas mileage. It needs to be fixed.