I was dealing with that P1507 code for months. I tried changing the neutral position switch and within 1 km the light was back on and my car was stalling randomly again.
Last thursday I decided to pull the IACV off(wow was it dirty!!) and gave it a proper cleaning and it has been working ever since. I sealed up the back end with duct tape, filled the unit with seafoam and then let it sit for a few hours. I then drained all the fluid out, cleaned all visible parts with q-tips and blew compressed air into the unit. Since then it's been idling perfectly, no stalling and no more check engine light.
Caschmidt, try cleaning your valve and see if that is indeed your problem, it takes less then an hour to do and the gasket only costs a few dollars.