I have a 2006 f-150 with the 4.6. The truck always starts well in warm weather, but in the cold of winter when I start it up it will start and then fall back to about 500 rpm for a few seconds then run rough and pull back up to around 1000. Once it has been started and run for a few minutes it would start up normal. Any ideas?

 

i ended up just buying a bigger battery for mine. factory battery was 5 years old, doing different things...dragging, taking longer to start etc. the bigger one barely fit, but it made all the difference in the world. dont know if this helps you or not. good luck.