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Discussion Starter #1
I was driving on the highway and my check engine light started flashing, so I wen to an auto parts store to check the trouble codes and came up with the P0304. After doing a little research on here, it seems like there are a few things I can do to diagnose if its a bad head or not, but it seems like the general consensus is that if its idling rough then its probably the valves, and if its not it may be a coil or bad plugs. Am I wrong?

Any help would be appreciated.

Its an 04 with the 2.8


Thanks, Jason
 

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a coil or plug is a possibility. try moving the coil to a different cylinder of the engine and see if the code follows. inspect the spark plugs while your at it. If all is good. You'll need to perform a cylinder leak down test.
 

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maniac mechanic
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Just because you have a misfire don't assume it's the head, especially on a 4 cylinder since that is rare, the 5 cylinders had most the issues.

Start by pulling the coil on cylinder 4 and checking the plug, if the plug looks fine then swap the coil with another cylinder and see if the misfire follows. If it does the coil is no good.
 

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I had this also on #1. Changed coils around and still came up with the same code. I changed out my upstream o2 sensor and it fixed it for me. Maybe something else but you will have to troubleshoot.
 
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