Question about my m air meter ''?

With the mods you have you shouldn't be having that kind of issue with the MAF. I've had cold air intakes on all the fuel injected vehicles I have owned all with stock MAF with no problems. Upgrading to an aftermarket MAF from somewhere like Summit Racing or something would be a good idea since it would give you a slight bump up in engine efficiency and performance but its not whats causing the trouble unless its just bad. Go to your local auto parts store and either buy or rent a compression tester your catless exhaust could be the culprit. Cats do decrease your exhaust flow but they also create back pressure and therefore compression in the engine and low compression would cause an issue like this. I'm not sure where you live but I'm pretty sure no cats on a 96 Mustang GT street car is an illegal mod anyway. To answer your question about tuning the MAF you would have to get someone with a programmer for a Mustang GT to connect to your computer port under the dash and adjust the ECM to better run with your setup, they might also be able to solve your idling problems too.