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    Thread: rough idle

    1. #1
      Should I keep it? red04fourdoor's Avatar
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      rough idle

      my 04 aveo has a rough idle problem with a po300 code. I see that my fuel rail pressure sensor says 0psi on my scanner. I know that's not right because it drives great. I can unplug the iac and get no change whatsoever. I only have the po300 code as well. I'm stumped! any ideas?



    2. #2
      Should I keep it? red04fourdoor's Avatar
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      anybody have an idea?

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      Almost time to do my timing belt
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      Misfire can be caused by a number of things, and you haven't said much about what you've checked so far. Plugs and wires would be the first thing I'd look at - have you checked those? You should list whatever you've already done, along with mileage and the recent history of other problems and repairs.

    4. #4
      Should I keep it? red04fourdoor's Avatar
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      haven't had it that long. always done it. going to replace plugs today because who knows when they were last changed. the only code is the one stated above. Also gonna change some vacuum lines.

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      Should I keep it? red04fourdoor's Avatar
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      anyone? any input?

    6. #6
      What do you mean there's no turbo? PoisonIvy's Avatar
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      Did you do the "spray a mist of water over the plug wires in the dark" trick? Personally, I wouldn't go changing vacuum lines unless they looked cracked.

    7. #7
      Should I keep it? red04fourdoor's Avatar
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      I changed wires and no change. some of the lines were cracked. I ran my scan tool again and noticed a few things. the map reading is 8-9psi at idle along with a throttle position of 14.5percent (???) at the same time. the load percentage at idle is way high at 40-50percent. I'm thinking vacuum leak or bad map sensor. If I remove the line to it while running It goes back to 14.5 psi (normal ambient air pressure) Also, my fuel rail pressure in relation to manifold pressure is 0psi. I have fuel pressure and it drives great at highway speeds and accelerates good.

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      Did you change the plugs and if so, how did they look?

    9. #9
      Should I keep it? red04fourdoor's Avatar
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      not changed em yet. had em out though and they had been changed not long ago. look lean. white insulators. very clean. all look the same too

    10. #10
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      Did you run a quick check to verify that the plugs were all producing good spark? Yes, a bad plug is not very likely, but it does happen. And seeing a good spark from all of them would tend to rule of the coil, as well. Then, if they're all producing good spark, I would do a compression test next. It's another thing that's easy to do, and given that this is a new-to-you vehicle with an unknown history, it would be good to know how the compression is. Autozone has a fuel pressure gauge in their loan-a-tool program, and you might think about doing a pressure test with a gauge as well. Personally I'd run every easy test before starting to spend $$ hanging on parts.





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