Do the following; with engine at idle, disconnect the IAC plug.
If idle drops the IAC is good but may need cleaning.
If no change, clean it in an effort to clear a stuck condition from age and gum/dirt.
The test is to get you to see what it is supposed to do and that is control air bypass so idle speed can be controlled within specified limits.
The 1506 is telling you the idle is out of limits.
Good luck.