p0303 i have replaced two of each each fuel pumps and spark plugs. what now? on 2005 Chevrolet Colorado

just this past year the check engine light came on. i had a freind check the obd code for the check engine light and it came up with a p0303. i replaced the spark plugs, the the check engine light turned off a few months past and it came back on again i replaced again all spark plugs with boots. the light went away for a few months, and just the past month it came back on again. im about to change the coil ingition and fuel injector if this continues what else do I have to replace for my engine to run normal so i can get my smog cleared and done.

by in Indio, CA on November 10, 2011
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1 answer
ANSWER by , November 10, 2011
You may have a problem with on of the valve seats, this has been reported as a common problem - http://repairpal.com/worn-valve-seats-may-cause-engine-misfire-115. Performing a cylinder leakdown test may be necessary to confirm this.