HELP! 97 Mustang GT 2V 4.6 Dies in Gear

The reason why your brother's 97 GT is dying/stalling because the 96-97's do not have the re-flashed software that comes on the newer GT's for example 99-04's. The only thing you can do is that when the car is bone cold, start it, and drive it for about 20-30mins. The computer is going to have to learn how to Idle under load in a gear and without it in gear. People, who have these year cars no what Im talking about. Its not uncommon about what your brother's problem is because it happened to me and my friend also. We both have 96 GT's.

Basically, its a very irritating/annoying but as soon as the computer learns, it will be fine. The sense able thing is to let it idle but as soon as the car is warmed up it wont be able to hold its rpm's when you put it in gear. So like I said, when the car is bone cold, start and drive for a good 20-30mins. If you have anymore questions PM me.

It could also be the IAC...