Outside Air Coming In Passerger Floor

The heater motor is under there along with the vent door, you can remove the glove box to take a look in there to see if there is something open that should not be. The blower motor resistor is also down there and a small piece to open to get in there, check if it is coming out there is so you need to check if they are properly in place. The heater takes air from outside under cowl grille, remove that and check if it comes in under there.