Fixed stall/rattle/bucking with AC on, braking/coasting below 30mph
 

My first post! So glad to finally pay it back...

I have a newish BRZ, production date Nov 2013. In neutral, with A/C on, while lightly braking, around 20-25mph, the engine RPM's would dip to about 550 for a second or two, then go back up.

If this sounds like your problem, please look up TSB 11-136-14, dated 3/26/14. "Reprogramming File Availability for Idle Stability and Extended Engine Cranking"

I went to a dealership twice about this, but only knew about the TSB the second time. Long story short, the service manager said he would apply the fix even though he thought it was not appropriate for my vehicle. Lo and behold, it fixed the problem (so far). Also, it is too early to say, but I think my Avg MPG calculation is less inflated now.

Edit 3 weeks later:
The reprogramming did not fix the problem completely. It still happens, though its less frequent.