A PO303 is a cylinder 3 misfire. It is most likely the cause of the PO316. The 316 just means that the PCM senses a misfire at start up (within the first 1000 revolutions of the engine). You need to check cylinder 3 to make sure the spark plug is good, the coil is good, and it is getting fuel.
Check it out and let me know what you find.
Saturday, May 24th, 2014 AT 6:36 PM