Rough idle and missfire codes

Roustabout · Apr 7, 2014

The truck has been intermittently running rough just after start-up. It will clear up and run fine after a few minutes. Most of the time no codes are thrown but I have had a brief flash of the CEL and codes P1300, P0302, P0304, P0306, P0308. Now since I’m getting misfires on both coil packs I’m leaning away from it being a spark plug/wire/coil issue. Should I start looking for a vacuum leak or dirty MAF? Will a fuel pump on its last leg cause this issue? The issue seems more pronounced when the truck has been running, then parked for hour and started up again.

Any suggestions as to what I should be checking (most probable to least)?
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jkempf · Apr 7, 2014

Mine was bad wires and old coil packs, happened especially when humid or left outside during rainy cycles. Warm start issues could be a fuel pump check valve or a bad fuel pressure regulator. Did you pull the vacuum line for the fuel pressure regulator to check if fuel is present? Did you check fuel pressure?

jafir · Apr 7, 2014

Codes for just a single bank would make me think o2 sensor. Someone once reported having misfire for just one bank being one plugged cat.

Roustabout · Apr 8, 2014

I checked for vacuum leaks using a stogie and found 4 small leaks; the dumb plastic clip for the vaccum line on right side of the upper intake manifold, 2 leaks between the MAF & throttle body and the butterfly valve. Pulled the right O2 sensor plug and it looked spotless and I noticed a little bit of soot at the joint between the cat and exhaust manifold(though I couldn't detect any exhaust escaping). I couldn't check the fuel pressure because my gauge is only good to 15psi. Haven't had any missing yet but I'll give it a few days and pickup a fuel pressure gauge. I don't believe I have a plugged cat as I haven't experienced any power loss under load.

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Rough idle and missfire codes

Roustabout

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jkempf

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jafir

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Roustabout

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