Minivan Stalling with check engine light on

My 1999 Ford windstar with 99,300 miles has the check engine light on and has been stalling in the mornings when I come to my first stop sign. After it has been driving a little longer it doesn't stall the rest of the day. I have had the car in to figure out the check engine light 4 times. They have replaced the 02 sensors and most everything else related to the code that came up. Still the light is on. I am wondering if the stalling is related to why the light is on? Or what I should ask them to check to stop the stalling? I am under warranty for only 800 more miles and need to figure this out fast! Thank you
The codes that came up werePO171 P1246