Most starting problems originate at the throttle body. My educated guess says that either your air mass meter is sad, your throttle body is gross, or a combination of both. If the throttle body is way "gooked up" (technical term), as the car warms up, the "goo" softens and kinda "oozes" out of the way and allows the throttle to work properly. Pull the air intake hose off of the throttle housing and peer inside. If it's pretty, silver, and shiny, unplug the air mass meter and see if it will idle for a longer period of time. If it's black and filled with "gook", clean the hell out of it and go from there.

Chris