Re: stalls when decelerating
MAF would typically cause more issues than just stalling on decel
A vacuum leak is possible but seeing as it's stalling more when you hit the brakes..
Try hitting the brakes when sitting at idle, see if the idle jumps around
If it does, it could be any number of things..
I'd say, as cleaning the IAC seemed to make a difference, that is the most likely cause - it could be the cleaning helped, but cleaning an IAC doesn't always fix the base problem (This may not be your case, but I've seen carbon gum up with carb cleaner, when not everything is removed it may cause issues with the IAC down the road)
That's where I would start
When braking and with the engine feeling like it's going to stall, try bumping the throttle a bit
Another thought could be the Throttle Position Sensor, but that's not as likely seeing as it only stalls if you're on the brakes
2012 IS F Blue IS F Sport
2006 Mustang V6 wannabe