OBD Sensor throwing P0304 code

TAY-CLEM

MEMBER
2001 KIA RIO
89,000 MILES

The engine runs fine while I'm driving down the road, but when I sit at a stop sign/light for more than 10-15 seconds, the engine starts to stumble. It also stumbles when I put the car into reverse. It doesn't stumble as much when I keep my heat/air conditioning off, or if I shift into neutral when stopped at a sign/light. I hooked an OBD code reader to my car and it threw the P0304 code. Is this referring to a bad spark plug, wire, or fuel injector? Or some combination of the 3?

3 Replies

JACOBANDNICKOLAS

MECHANIC
108,355 POSTS

A PO304 indicates a #4 cylinder misfire. It could be a plug, wire, fuel issue, compression issue. Have you checked any of the items mentioned yet>

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Thursday, December 8th, 2011 AT 11:05 PM

TAY-CLEM

MEMBER
16 POSTS

I have checked the spark plug and wire. Both look to be in good condition. I put fuel injector cleaner in my car about 3 days ago, and it seemed to help a little, but not much.

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Thursday, December 8th, 2011 AT 11:18 PM

JACOBANDNICKOLAS

MECHANIC
108,355 POSTS

See if the injector cleaner continues to help. If it doesn't, you may want to check the injector on cyl 4, check engine timing, and check engine compression for that cylinder. Since it seems to miss under a load, it could be any of the items I mentioned.

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Friday, December 9th, 2011 AT 3:28 AM