96 Electrical problem

Intermittent (about every 3 weeks) problem with car not wanting to idle high enough to keep the alternator output up. When the gas is let up, the idle rpm drops to about 5-600 rpm and the alternator goes from 14-15 volts down to 10-12 volts and the car dies. This seems to only happen when the car is left outside in moderately cold temperatures (20-40 F). Car doesn't die if the transmission is shifted to neutral and a little gas is given. After the car dies 2-3 times, the check eng and transmission lights come on and the car goes into the limp mode. If the lights are reset, the transmission returns to normal operation. Down loading the electrical system (turning off ac, lights, radio, etc does not seem to effect this). Is this an indication of an electrical problem or something in the fuel scheduling??