My battery light came on and ended up Replacing the Alternator. All is well.
However....for several weeks, the idle speed has been fluctuating from normal at 650rpm up to 850-900rpm's. Sometimes if it was idling high you could restart the truck and it would idle normal again. But by the time you got to the next light it would idle high again. Could not figure out what was going on and there were no codes.
This past weekend the battery light came on so I had the alternator tested and it tested bad so I replaced it.
Battery light no longer comes on and the truck idles normal at all times now.
Was thinking that the alternator was failing all along and that's why the engine would idle higher to get voltage up from alternator.
Anyway... thought I would share my experience about the engine idling high..
All is well now till my rebuilt aftermarket alternator fails....and it will cause they aways do.

 

Good to know, what did you put in and what did you pay?