Car stalls on low idle/shifting gears after cold start, but runs fine after 10 min warmup

[dbablitz]

Recently my 2010 Subaru Impreza has been stalling. If I turn the car on first thing in the morning, it turns on and idles fine in park, but when I put it into reverse, unless I rev the engine it will shudder and stall. Even if I get out on the road and shift into drive from reverse, if I have to come to a stop within the first 10 min of driving, the car will stall when stopped at a low idle. The car keeps turning on so fairly certain it's not the battery or alternator, but my knowledge of engines is limited at best. Only other ideas are worn out spark plugs, o2 sensor, vacuum hoses, or maybe moisture in the fuel from the cold. Any ideas/thoughts/advice? Thank you!