I would start by doing a "psychic reading" or interpretation of the engine's operation characteristics. When the stall occurs, does the engine stop instantly like it does when the ignition switch is turned off? Or, does it surge, or drop in rpm when you shift into reverse, and just seem to be running too slow?
First of all, when started, the engine speed should go up to around 1500 rpm for a couple of seconds, then come down to normal. This "idle flare-up" proves the idle speed motor is working, the air passage around the throttle blade is not blocked with carbon, and the engine computer has control of idle speed. If this does not occur, there could be a problem with the idle speed motor system. Further evidence would be that the stalling does not occur if you hold the gas pedal down 1/8" when shifting into reverse.
The engine computer also commands more fuel to be delivered in cold weather. An inaccurate reading from the coolant temperature sensor or ambient air / battery temperature sensor could result in too little fuel to maintain proper engine speed.
Automatic transmissions need to develop much higher hydraulic pressure in reverse. That puts more load on the pump which increases the strain on the engine. That is one possible reason the stalling occurs in reverse. Another is the rocking of the engine that could lead to wires in a harness rubbed through and touching bare metal where the paint has rubbed off. The harness under the battery tray is a good suspect.
Due to the throttle position sensor code, another good place to check is electrical connectors between the engine and body. Wiggle and flex the connectors while watching for the engine to stumble or sputter. Your mechanic can connect a hand-held computer to read the sensor voltage while he tries various things to make the voltage change. The least likely suspect is the sensor itself. It would cause a stumble when you are cruising and the sensor is moving with the gas pedal.
Related to corroded connector pins and bare wires rubbed through, try pushing the car forward and backward while it's in park and the engine is running. That will rock the engine and make the wiring harnesses move and flex.
If the engine stalls most of the time when you shift into reverse, I'd be leaning toward a wiring issue. Plus, it will stall after you feel the clunk of the transmission engaging. If it only happens once in a while, and mostly when the engine is cold, I'd suspect insufficient fuel or idle speed is too low. And, it might stall before you feel the transmission engage.
As for the other fault codes, forget about # 12. That just means the ignition switch was turned off. If you have the reliable 3-speed transmission, the speed sensor is the likely culprit for the intermittent speedometer.
Tuesday, January 19th, 2010 AT 1:37 AM