Toyota Repair: Soft brakes, engine wants to stall, rear brake drums, power brake booster

Question
I have a 2001 Camry 4 cyl. automatic.  The brake pedal went soft  5,000 mi. ago. When stopping, the idle speed would decrease and the engine would run rough. The rear brake drums were cleaned of dust and the problem went away.  The same problems are back. I tried backing up at 20 mph and using the brakes hard to readjust the shoes. This solved the soft pedal problem. I took it to the dealer who did an inspection of the brakes and found nothing wrong except the front disc pads, which he replaced, even though they were greater that 2/32" thickness.  The brakes worked fine for 2 days. Now the pedal is soft again, braking distance is longer, and at least once the engine wanted to stall after gentle braking and turning slightly to the left.  Please help.  Thanks.

Answer
There may be a problem with the power brake booster or the vacuum hose going to it from the intake system which is indicated by the engine wanting to stall, brake boosters are expensive so you should have someone that knows brake systems inspect it.