Hi guys, new to the forum here. Ive got a worrisome issue here and im a bit stumped. Dont really want to throw parts at this. I purchased a 1991 Mazda Protege (1.8 L4 SOHC, manual) about a month ago. Car still runs with 183XXX miles on her. Shes had an issue idling erratically (revving up and down) pretty much since ive owned her, temporarily fixed it (after bleeding air from coolant), but now its back and getting faster. Noticing that the coolant gets almost boiling hot while she runs from cold for like 5-10 mins (thermostat issue maybe? Water pump? Not seeing any overheating issues on the dash). Only idles erratically in neutral or with clutch in. Ive noticed that the only time it evens out is when the cooling fan kicks in (AC ON), then it idles fine. It used to be a bit hard to start, but not really seeing that issue anymore.

List of things ive done, in this order:

8/18/18 oil change 182439

8/20/18 cleaned TB, IACV, MAF, Intake duct -> threw code 15 (O2) 182501

8/25/18 coolant flush, refill and bled (fixed idle issue for a while), iacv gasket replaced, tps replaced, coolant temp sensor replaced, seafoam added to gas tank 182612

8/29/18 misfire suspected, diagnosis began, checked injectors/plugs/wires/fuel filter/vacuum leak, no luck. Started her back up a few days later and no more misfire, hasnt since 182300

9/2-3/18 O2 sensor replaced, valve cover gasket replaced, coolant replaced, lower and misc. radiator hoses replaced, valve cover bolts replaced (because two snapped from overtorque), oil check, IAAScrew adjusted, cleaned around plugs/wires, tightened transmission bolts 183095

9/5/18 IACV replaced, bled air from coolant, closed IAAScrew

Looking at the manual, they say it could be vacuum leak (dont think so, checked with brake cleaner while running), leaking EGR (dont think so either, dont know how to check), air filter clogged (new filter), fuel pump (unlikely since it starts and runs fine when fan kicks in), leaking head gasket (likely since seeing white smoke sometimes, but dont know how this would cause a surge), timing belt/pulleys worn (doesnt appear to be worn, but idk when it was replaced last), camshaft lobes worn (didnt see much of that with valve cover off). Doesnt really say anything about the MAF, IACV, etc, which is strange to me because those are all issues that seem logical, but doesnt mention them.

Dont really know what i want to do next. Dont want to have the car sitting for a while with the head off while i try to replace the head gasket (if that is indeed the case). I may just run it with the fan going and run the car into the ground. Any input would be most helpful. Thanks!