Help - code P0306

got this 1999 4runner that is acting up. Car runs well until it gets warm than it starts to rattle, and does not have much power.

run the scanner and got Code P0306 misfire on cylinder #6. changed the coil and the car is still doing the same thing... it appears that it does that after the car gets warm, like it runs for more than 20min or so.

there is oil leaks around the head gasket and am wondering what could have caused it? Changed the PCV valve, new air filter, will put sparkplugs new ones. Any thoughts? Some friend was saying it's the fuel injector, but i just don't get it. Why it runs well when cold than after it warms up it starts to act up?

 

have you taken it in to a mechanic for any additional tests? compression, leak down, coolant or oil tests? could be a list of issues