I'm trying to troubleshoot a high idle issue (when the engine is warmed up).

*TPS adjusted correctly
*Fresh coolant, new thermostat, air bubbles have been burped from system.
*All vacuume lines are routed correctly and in good shape
*AFM has not been touched*
*Idle mixture screen turn the entire way in
*Not throwing any codes

With the idle screw in the entire way it idles around 1500 RPM's.

Here's the kicker, I took the truck out wheeling last weekend and it idled where it should the entire trip (in fact, i had to turn the idle screw back up where it was previously). It would only idle fine while crawling / staying at slow speeds, which was over 5 hours this day. About 5 minutes after I hit the paved roads I pulled in into neutral and it was idling at 1500 again.

I'm thinking it's sensor related; the coolant temperature sensor acutally. Since this is an uncommon thing to fail I thought I'd get some feedback before I pick one of these up.

What is the ignition timing set to?

Also, is the throttle plate fully closing? Linkage should make contact with the stop screw.

With the diagnostic terminals jumped I set it at 5 degrees.

The throttle body has been cleaned, it's contacting the stop screw. In addition, i removed the dash pot, cleaned, and lubed it properly.

Might then be something temperature related as you noted. Could be the ECU sender is a bit off (reading too low a temp) and when you went wheeling, the temperature in the coolant went up a little and that was enough to kick the ECU out of fast idle mode. Or it may be the idle air valve is doing something similar. Or the thermostat may be too cold (or opening too soon) and that is making the engine run too cold.

Yeah, I agree with the coolant temp going up slightly while wheeling; enough to bring the idle back down to normal. To go along with the this if I shut the truck off and start it back up 5 minutes or longer it will idle normal (acutally lower than normal since the idle screw is in the entire way - again, this is because the coolant is slightly warmer now since it's not being cooled).

The thermostat was replaced with a 190 degree toyota stat; I don't think that's causing the issue.

*Update*

I replaced the Coolant temperature sensor last night without it making a difference.

I'm pretty stumped at this point. One other note is that this problem occurred shortly (2 weeks) before the headgasket went. Since I was loosing coolant before this I put in a good bit of Radiator stop leak to delay the inevitable.

After this I did a complete rebuild on the engine; I'm starting to think that possibly one of the smaller coolant lines could be sludged with the stop leak or something?

Any other ideas?

The 22RE does not have a ECU controlled idle speed so I would start with the basics looking for any way air can bypass the TB like the idle air control in the TB and AC idle up circuit.

Take a look at page 8 here: http://www.autoshop101.com/forms/h21.pdf

Thanks for the link.. the Thermo Valve inside the Idle air control thingi sounds like the culprit.

I took the throttle body off and cleaned everything the best that I could, which needed cleaned anyway... That didn't seem to help but I'm going to give the idle valve the test by blocking the port while it's warm... if it's defective then it should drop the RPM's back to normal.

I'd hate to fork out 150 bucks for a new Idle control assembly but I think it's necessary because I can't find just the Thermo Valve (which is removable from inside the entire assembly).

mine idles high sometimes and sometimes not- i found that if you just give the accelerator a little tap, it drops down to normal.
my cable is most likely clogged with sand.... just like everything i own.

sorry if i am throwing out a stupid simple thing but sometimes it is just something like that.

May be a dumb question, but did you try to close the throttle plate by hand? Or maybe a simple (not simple to find necessarily) vacuum leak i.e. hose etc?