I'm still chasing a high idle issue which I think may be my ecu in need of a resetting after a conversation with the stealer. There may be one more possibility. Just above my iacv and my tps there is a metal looking washer with a Philips head screw sticking out of it. I don't think it's supposed to be there and it seems stripped. I know not a very accurate description. I took a picture with my phone but am unable to attach it.
On second thought the washer appears to be a blank with a screw drilled in slightly on an angle.

 

Can also be coolant temp sensor out of range, making engine think it is -40F outside. Is your truck old enough to have an OBDII port, if so a scanner will show you the temp and if it is changing. This is done by a sensor separate from the one that drives the temp gauge.

 

I had a persistent high idle that drove me nuts for months. Two weeks ago I had the ECU adaptive values reset. So far so good and its very nice to have a normal idle again. Much better on has mileage too.

 

Thanks guys, I have an ultragauge coming in the mail today or tomorrow and an appt, for the dealer on Wednesday.

 

In the mean time, do not mess with that idle adjustment screw or you will have a whole bunch of issues. Need to get your codes read and get back to us with your fault code numbers.
Have you already cleaned the t/body and the IAC?

 

Mike, my troubles started after the cleaning. I have an older thread about it. After speaking to the dealer he said it probably does need a reset. I also don't have any codes but my ultragauge should be here tomorrow so maybe I'll be able to dig a little deeper with that. Again she idled beautifully before cleaning the iacv.
List of what I did:
Cleaned tbody, replaced iacv, replaced tps, used starter fluid to find vac leak.