Temperature ups and downs?

[JKJ82]

Haven't had the truck very long. A few weeks. Can't figure out why there are times the engine bay gets so hot, other times fine. Popped the hood today and went to touch the hood prop bar, and it burnt the heck outta my thumb. That hasn't happened since I've had the truck, and it has been fully warmed up many times I've touched that prop bar.

Weird. I noticed it only seems to get way too hot when it wants to idle high. It idles ok sometimes, and other times it idles in park wayyyyy way too high. Funny thing is when I drive it, it has been fine so far with how it idles at a stop, it only seems to do that when the truck is in park. And, it doesn't do it all the time.

I'm absolutely stumped. Any ideas???

 

[19Walt93]

What does the temperature gauge read?

 

[SenorNoob]

If the engine is getting so hot that the prop rod burns you, I'm surprised it hasn't blown.

Not sure if it's relevant here but a small engine revs higher as it runs out of fuel (getting leaner). Also leaner is hotter. I'd suspect some form of intermittent vacuum leak