this ones got me puzzled, suddenly the other day after no changes to the truck i started it and after about 5min warm up the idle will get stuck wherever it's at when i shift to neutral or press the clutch.

so if i'm driving and at 2500 RPM then shift into neutral it will stay at 2500 RPM with my foot off the gas. it stays exactly at 2500RPM for ever (or at least for up to 20 min that's as long as i tested).
However if i am coming to a stop and the RPM is lower, say 1000 and i shift to neutral it will stick at exactly 1000RPM. i can rev it up but as soon as i let off the gas it goes right back to 1000RPM.

i confirmed that the throttle cable is not sticking and the fact that it doesn't start this until after it's warmed up does seem to point to IAC valve, but i have had that go south before and it had a more random high idle and low idle. idle does not loop even when at 2500+ RPM like it would if you adjusted the idle too high.

 

Do you get a CEL?