Hey guys

I have an 03 Civic Ex.
and my check engine light came on yesterday. So I took it to Auto Zone to get the codes checked out and I got P0301-P0304. Has any one had this problem before? I last changed the spark plugs on Jan 10, 2014. But I also changed my cam that day as well. I'm no longer stocked. I don't want to go changing everything at once if anyone has had this problem? and if so what did you guys do first?

 

OEM NGK brand spark plugs are best in your civic to reduce the occurrence of misfiring.

If you have el cheapo plugs other than NGK, I would look at these as the source of your misfires first.

Next, while idling, remove the connector to each of the ignition coils one at a time and observe if the idle changes to rough. The coil that does not show a difference in idle is the faulty one.

Check these 2 areas first before moving on to the injectors.

Other areas to look into are bad gas, any other codes than the misfire ones, Seafoam treatment, leakdown test of cylinders, vacuum leak and fuel pump.

Sure hope it's simply just plugs or coils.

HTH