P0452 & P0300 CODES

P0300 are misfire codes, so the first thing to check is the condition of the coils, the wires, plugs, cap and rotor. The P0452 is for the Fuel tank Pressure Sensor. This has to do with the Evaporative Systems Self test and will not effect engine performance.

check your mass air flow sensor on the 3 small heated wires - clean them with brake clean lightly using a q-tip I had the same problem - let me know

The PO300 misfire under heavy loads is often the first sign of a weak fuel pump. The fuel pump is not delivering enough volume for all cylinders to fire properly at WOT (wide open throttle). This is a common problem with aging and many aftermarket fuel pumps, replace with the factory pump assembly.

Could be as simple as a clogged fuel filter. The fuel pump could be working properly but the filter is restricting the flow that would only show up under load. Would drive fine under part throttle but when the throttle is opened up there isn't enough fuel. Hope this helps. Fuel filters are often neglected. Another thing would be to but a quality filter like a Hastings. You can also try and blow some air thru the new filter and then thru the old filter and see if that's the problem. Roddy