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The P0450 code will not cause any performance issues. If you do not need an emissions test done in order to get your license plate renewed I would not worry about that at this point. P0301 is a cylinder misfire code along with P0304. You need to inspect the ignition wires coming from the two coil packs and the ignition spark plugs. Try swapping the spark plugs to cylinders two and three which are the middle to cylinders. Cylinder number one is the cylinder closest to the passenger side. Ideally you need to check the compression on all four cylinders also. This engine has had some issues with ignition coils. Cylinders number one and four are operated off the same coil pack. It is possible that this coil pack has gone bad. Check for spark coming from the coil.