Why are we doing this? Normal idle is 700. But I find if I leave the truck idling for any length of time (say I started it but then went back inside for something) I'll come back to find it idling at 1200ish? If I step on the brake pedal, it goes back to 700 rpm.

???

 

my truck does the same thing if it's really cold out

 

Doesn't have to be really cold.... Or even a little cold....

 

Well, I'm from California. So really cold to me is in the 20's to 30's. I see you are from Maine, I'm sure you have a different opinion on what cold is! My truck has done it in when the weather was in the 40's too

 

I cant say for sure 100% but I think it has to do with the EGR system.

I know our big rigs at work will idle up on their own to keep the egts hot to perform passive burns.
I don't see why our trucks wouldn't do it themselves.

 

I stopped and was unloading a load of grain yesterday and my engine water temp was 205 and my truck idled up and it is fully deleted

 

Fully deleted only means you are fooling the computer. The system still thinks the EGR is there. Unless you have swapped out a ECM and or flashed the ECM to a different version non EGR.
All the programmers do is fool the ECM into seeing values within spec.

Your engine needs to run within certain specs for a burn, those are Coolant temp, RPM, exhaust temp, pressure and a couple others I am forgetting about

In order for your engine to do a burn it needs to meet those parameters, so when it idles up, it is manually getting up to those temps/settings to do a burn.
You don't notice it while driving your truck because your truck already meets those parameters.

 

There was a flash that came out in late 2009 for a Soot Reduction Strategy. The engine was set to go to 900 rpm from 700 during extended idling. The cold idle warmup is 1000 rpm. 1200 Rpm is only enacted with manual selection from the cruise control circuit.

I have mine deleted and doesn't idle up unless its cold. It does matter what programmer you have whether or not the soot reduction idle is still active.