P0305 on daughter's 05 Pathy LE

[Jeremyda78]

We recently purchased a used 2005 Pathfinder for our daughter to drive as her first vehicle. It's a great vehicle but has a misfire (P0305). We took it to a mechanic who thought it was the fuel injector so he replaced it but after driving it on the interstate the misfire came back. Since then we have changed the spark plugs, replaced wire harness, replaced catalytic converter on passenger side, replaced manifold gaskets, replaced throttle body and gasket, replaced valve cover gasket (there was a leak). It idles fine at first but after getting warm and reving it up it begins to misfire. We used Cataclean prior to replacing the catalytic converter and it ran great for a couple of days but then the misfire came back. At a loss as to what is going on.