I just bought a used 05 Tacoma with a cyl4 misfire

I just bought a used 05 Tacoma with a cyl4 misfire
I just bought an 05 double cab tacoma with the v6 and when i test drove it the check engine light was on asked the dealership about it they didnt know anything about it and it was a sunday so service wasent there but it was a mazda dealership. We bought the extra warranty on it so anything should be covered. Bought the truck got it home took it to autozone they checked the code and it was cyl 4 misfire

so the obvious things came to mind plug, wire, coil etc. checked the car fax and low and behold right before we bought the truck about 2 weeks before they replaced the head gaskets and plugs new serpentine belt radiator flush. So tonight after almost a week of driving the check engine light is now off. But when I looked under the hood and checked the exhaust manifold header bolts, they are as rusted as a 2 dollar hooker. No way did they take them off to replace the head gaskets unless there is a way to leave the header on and pull the head off. but now the check engine light is off not sure if maybe the computer finally corrected itself or what but now im wondering what i got myself into $17000 hot mess.. any suggestions or ideas about why the check engine light would go off if it was still having an issue?

 

Is the truck actually experiencing a misfire (i.e. abnormal vibration felt and heard)? Hard to diagnose something if the symptom went away.

 

in the mornings when its cold it idles a little bit rough but smooths out after a 20 seconds.. but thats when the light was on i mean it has been on since we left the dealer lot and now its off so i guess in the morning i will try to start it see what happens but it would seem logical that a misfire code would not just clear itself up if there was a legit problem.. my theory is the mazda dealership did the work and maybe forgot to reset the computer or maybe the plugs were not replaced after they pulled the head and the plug maybe cleaned itself up and is running but its strange every day without a thought that check engine light was on from startup cold, warm every time now after driving it all day its off.. when i got home i turned it off and started it again to see if the light kicked on but it didnt..

 

i couldnt help myself when i seen her, she is purtty just want her to last awhile.. I wanted this over a dodge but seems like i might have got a hot mess