High idle and stuck thermostat

Hey y’all, I’ve got a 2013 Tacoma V6 and when I start it, it goes to about 1800 RPM and settles at around 1500 and won’t go lower until put in gear. It’s done this once before and I just had to unplug the battery and plug it back in and it idled normal again for 200 or so miles, but now it’s doing it again. No check engine light. The truck also won’t get in the temp gauge past probably 1/5th even after driving the truck hard in some backroads to try and get some heat in it and it just refuses to go past it. The heat is turned off when I’m doing that and if I turn that on it drops the temps down to the C. Any ideas on either issue? I’m kinda clueless on the first one but I assume the 2nd issue is a stuck thermostat.

 

Step 1 is to check the coolant in the radiator (not just the overflow bottle) and verify it's full.
If your coolant is full, heater doesn't work well, and your engine won't come up to temp most likely the thermostat is stuck open, if the heater works good but the engine temp is reading cold you may have an issue with the coolant temp sensor.
The high idle is almost certainly related to the coolant temp problem, idle learn doesn't begin until the coolant temp gets to about 174F.

 

From what I can tell the truck is good on coolant. The truck has a decent coolant leak that I haven’t pinpointed yet also. The idle today dropped to about 1200 but it’s also about 20 degrees warmer today. The heat works okay but not great as well.