Originally Posted by Forbidinworks
This is a shot in the dark but I am wondering if this could be caused by a leak in the brake booster?
A leaky Brake booster will tend to increase idle speed not decrease.
Also, the voltage drops because idle speed is decreasing. Slower idle means slower alternator speed. Alternator output is a function of rotor speed and strength of field.
For the stalling, Check your EGR valve it might be sticking or your idle air control valve could be dirty or your base idle is not set properly.