Erratic idle, overheating?

[KTMrida4life]

So my S14 is totally stock. It has 26000 miles on it as of a few days ago..

Heres the problem. It had only happened once every 3-4 months or so, but now its starting to happen almost once or twice a week. The cars idle is very erratic. Sitting still, it will go from 700, to 1000, down to almost where it stalls, sometimes it will idle high (1500), and not to mention when I turn my system up (put a load on the alternator) it bogs down really bad and almost shuts off. Its not voltage drop because I have a voltage meter and am staying well above 13V.

Heres the other thing it does. Sometimes when I stop, I will look down after a few minutes and it will be overheating.. almost all the way on the H on the temp sensor. If I drive around in circles for a few seconds, it immediately goes back down to the middle. Im fairly sure its not actually overheating.. Im not 100%, but Ive had it overheat before and it started shaking and steam came out from under the hood. Also if Im not mistaken this car has a mechanical fan which is always being turned by a belt.

Whats going on here? Is my coolant temp sensor fubar'ed? Would that cause the engine to *think* its overheating and make the idle erratic?