High idle 1993 3vze pickup
 

I'm sure this question has been posted to this forum before, but I can only search for so long.:gamer:
One morning a couple weeks ago my idle ran and stayed at 1,500rpm (the idle and rpm were literally perfect before this day), I know once the coolant reaches a certain temperature, the idle should drop down to around 850rpm. There is no check engine light on, but for giggles I checked the code anyways, and all systems are normal. I checked the vacuum lines and even had my mechanic take a quick peak at it, all looked good. I checked the coolant level as my mechanic said a low coolant level can cause a high idle (I forgot the reason). My brother and I did a valve job on the driver side head summer 2017, and while we had it apart we replaced the engine coolant sensor as well as the other switch and sensor located in that same location (I forgot the names). Of course we replaced all the vacuum lines and most of the coolant hoses as well. Then I had the head gasket on the passenger side done just a few months ago. I did adjust the idle screw, which gave me the 850rpm idle, but then I didn't have the high idle, which was fine until this weekend as the temperature is dropping and the mornings are a bit cool now. I'd like to do what I can to figure out the issue before I decide to drop it off at my mechanic, as funds are tight and I don't have an extra vehicle around. Any help and ideas are much appreciated, thank you in advance!