MAFs are not hard to di-ag if you know how to di-ag them. why are you in this section?
if your cat is glowing red that means its getting way way to much fuel. why did you just change out 1 injector and why. sounds to me like you have a injector wide open all the time. which is either a stuck(highly doubt it) or a short causing it to stay wide open.
does your exhaust smell like raw fuel and your cat still glowing? they you are running stupid rich.
you might want to have someone that knows what they are looking for help you out and look at the car.