I just did an engine swap in my 2001 F150 4x4 5.4L. I put a 5.4L out of a 97 Expedition 4x4. The check engine light is on. I used a scanner and it said i had a bad IAT (intake air temp.) sensor so i replaced it and the check engine light is still on. Also when i come to a stop the truck's RPM's goes to about 4-500 RPM and attempts to die but doesn't. The truck also shakes. Any ideas?

 

Rookie mistake!
Codes don't tell you what to replace in nearly all cases.
It only tells you what 'system' is in trouble.
There are many parts to a system. It could be any one or more parts.
What is/are the code/s?
Your may be discribing two different issues.