PO304 CEL at idle - Trying to figure out what is wrong - any ideas?
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This is a discussion on PO304 CEL at idle - Trying to figure out what is wrong - any ideas? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hello all, I have a 2002 WRX with 162,000 on it. I bought it a few weeks ago and I ...

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    PO304 CEL at idle - Trying to figure out what is wrong - any ideas?

    Hello all,
    I have a 2002 WRX with 162,000 on it. I bought it a few weeks ago and I just started having some issues with it. On my way to work last Friday, the car started to bog down and then my CEL started flashing. I pulled over and shut the car off. From previous experience on another car, i knew the car was mis-firing. I let the car cool down a bit, and then started it back up. The code was gone, so I decided to drive the car back to my house. about half way back, again the CEL started flashing when I was at low RPM. If I downshifted and kept the rpm's above about 3k, the CEL stayed on, but did not flash. I got the car home and parked it.

    Using another car, I got a ODBII reader and read the codes. I had mis-fires in all 4 cylinders. I reset the ECU by disconnecting the battery and holding the brake petal down for awhile. When I started the car up again, it ran fine for a few minutes, then the CEL started flashing again. I read the codes again and was just getting P0304 (mis-fire on cyl 4). I repeated this a number of times to try and get other cylinders to mis-fire, but could only get cyl 4 to give me a code.

    Yesterday I replaced the spark plugs with new NGK-G-Power plugs (#7092) gapped at .030. Same P0304 code.

    I then switched the coil packs from cyl 2 and 4, and still P0304 code.

    At this point i'm not sure what I should do next. I was thinking about doing a compression test to see what the results were. If that turns out ok, I think it might be a bad injector? I took a look at how to replace the injectors because I thought i might just switch the cly 2 and 4 injectors to see if the problem followed, but doing that is a ton of work.


    Let me know what you all think. Thanks for the help!

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    Registered User TrailerTrashed's Avatar
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    try some fuel injector cleaner. It's a cheap start, and with that many miles it might be due.
    Run your gas down a bit, throw some in there and open it up a little bit to the gas station to try and get some of the build up out of there.

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    get your valve shims checked

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    Registered User srcjrs's Avatar
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    pull the plugs and see if #4 plug is all jacked up. That's the hottest cylinder right off the up-pipe and will show the most adverse effects if it has ever run lean say from bad mods with the previous owner. Hopefully you don't have a burnt valve or damaged piston. Good luck with it, man, that code and issue stemming from a K&N intake causing poor MAF signal caused #4 to burn a hole in a valve and need a new head on my friends 02 wagon...
    Wagons Rule!

  6. #5
    Registered User srcjrs's Avatar
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    ^^
    sorry, I posted before I read your whole first post...I didn't see that you already did the plugs. Did the ones you pulled out look newer or did they show alot of wear?
    Wagons Rule!

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    #4 is the on the driver side rear. not related to the uppipe at all. i've gone through this already. check your grounds as well. but in the end, it was the valves. you have a 02 with high mileage. its just a matter of time before it happens

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    Moderator Donkey's Avatar
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    Search " misfire". This question gets asked every week.
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    So Tonight I did a compression test. I think it's a bad sign that something (valves?) is really wrong. Cylinders 1-3 were good, around 160 PSI, but cylinder 4 only read 15 PSI. What should my next step be? I am willing to rebuild the engine, but i've never done it before. Thanks for the help and suggestions.

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    sounds like you have some damaged ringlands. get a leak down test as well to see if you have valve issues as well

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