When I first saw these codes when my check engine light came on I started reading and watching videos as to what the problem may be. I replaced all of my spark plugs, tested all of the coils. Here is the strangest thing of all, in everything I have read in regards to missfire codes you should be able to tell you have a problem on how your car is running, however my car is running as good as it ever has !! no shaking, no rough idle, runs great !!

Does anyone have an idea as to what the problem could be ?

 

Try swapping coils to determine if the P0304 code moves to another cylinder.

Could be a number of issues. Check the simple things first such as air leaks for vacuum hoses leaks, intake and exhaust system and PCV system.

Hows the engine idle at cold and hot start?

 

engine idle is fine at cold and hot start. Also swapped coils and still shows PO304. Starting checking for vaccum leaks but can't find any.

 

Could be No 4 injector needs cleaning.