At some point after a few local hops to run errands, the engine won't start and hold an idle without my manual intervention - a constant light press of the gas pedal. It'll stall out on the highway if I let off the gas and coast...

Once this condition starts, it won't clear up until I park it for awhile and let whatever causes it clear up. I suspect one or more components must fault when they get too hot, just not sure which one.

Local service hasn't been able to diagnose it unless I bring it in whil it's ongoing - not an easy thing to manage. I've read a few items about the IAC sensor going bad, which associated similar symptoms.

Many thanks in advance for any advice or suggestions.

 

Here is a link to another poster about the same problem.
Air bypass valve. Should fix you right up.
https://www.ford-trucks.com/dcforum/explorer/552.html
Dialtone

 

Thanks, I found a number of other IAC mentions across the boards as well.

If a clean and check of the IAC doesn't clear up the problem, where do I head next. The EGR valve or MAF sensor?

I'm not getting a 'check engine' light when the problem occurs, so I don't suspect that I have any error codes to rely on.

 

If the IAC work doesn't check the intake manifold for leaks. This is usually expressed in the manifold gasket between the plenum and the heads. Also check for large vacuum leaks. High idle problems can also be caused by the throttle body itself. My '92 F-150 throttle body was worn such that it did not seat properly with the throttle closed causing an increase in intake air. The ECU seeing a discrepency between the throttle position sensor and the air volume tries to compensate by increasing the RPM until it is equalized, or the rev limit is reached. In all these cases it is caused by too much air. If the IAC cleaning doesn't fix your problem do not buy a new one until you have ruled out the throttle body as causal. A new IAC (about $70) comes with the replacement throttle body (about $250).