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Rough idle

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by EmAitch, May 4, 2018.

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  1. EmAitch

    EmAitch New Member

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    my 07 with 234k runs great EXCEPT at idle, like it can’t decide whether or not to shut off. I’ve noticed this getting worse over the past year, now it’s started throwing misfire codes. Recently had the cat replaced (threw that code, and was experiencing symptoms that made sense). The mechanic talked me into replacing only one of them, and I’ve experienced a huge increase in acceleration, as well as a drop in speed of battery depletement. Plugs are good, coils are good, cleaned air filter and throttle body. Could the idle screw have simply backed off over time? Or is whatever switch that controls whether it’s on or off be going bad?
     
    #1 EmAitch, May 4, 2018
  2. EmAitch

    EmAitch New Member

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    I neglected to add that I’m experiencing some blow-by at the oil filler cap, and recently changed the PCV valve. I had some pooling of oil in the intake manifold, and oil consumption has been rising for some time. I assumed low compression would also show up as a lack of performance, but maybe I’m wrong.
     
    #2 EmAitch, May 4, 2018
  3. edthefox5

    edthefox5 Senior Member

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    No idle screw it’s a fly by wire throttle body. Has a motor integrated into it. Pooling of oil in bottom of intake is normal in a g2. My brand new 07 did that.

    Answer this. Have you ever run the engine so low on oil it threw a red light alarm on the dashboard or a red light was going on and off because of low oil?
     
    #3 edthefox5, May 4, 2018
    Last edited: May 4, 2018
  4. cyberpriusII

    cyberpriusII Prodigyplace says I'm Super Kris

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    Clean the MAF, easy task. Might do it. 0
     
    #4 cyberpriusII, May 4, 2018
  5. SFO

    SFO Senior Member

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    Are you still running on the original HV battery after 234k?

    Sometime when a battery is failing the engine might continue to run when the vehicle is at a stop. The engine may also repeatedly cycle on and off while stopped. Usually this behavior isn't noticed in a healthy battery unless the heater or other accessories are being used.
    Which device are you using to read these thrown codes, and which codes have you retrieved?
    Curious what code was thrown, and which cat was replaced. Would be nice to know for future reference.

    Over time the rubber on the coils can degrade and allow for carbon tracking and misfires, you might try inspecting the cops, rubbers and plugs for telltale signs.
     
    #5 SFO, May 5, 2018
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  6. JC91006

    JC91006 Senior Member

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    I suggest cleaning your throttle body
     
    #6 JC91006, May 5, 2018
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  7. audiodave

    audiodave Active Member

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    #7 audiodave, May 5, 2018
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  8. cyberpriusII

    cyberpriusII Prodigyplace says I'm Super Kris

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    OP noted in original post that the throttle body was cleaned....
     
    #8 cyberpriusII, May 5, 2018
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  9. edthefox5

    edthefox5 Senior Member

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    Replaced clogged cat and saw performance improvement tells me it’s a big oil eater too.
     
    #9 edthefox5, May 5, 2018
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  10. padroo

    padroo Senior Member

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    Oil and coolant can contaminate the O2 sensor.
     
    #10 padroo, May 5, 2018
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    Oil pooling below the throttle body might also be fouling the Manifold Absolute Pressure sensor, assuming it's in that vicinity, per 3rd gen. Not sure the ramifications of oil-saoked MAP?
     
    #11 Mendel Leisk, May 6, 2018
  12. SFO

    SFO Senior Member

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    2nd generation Prii were stuck with only having a MAF sensor :(
     
    #12 SFO, May 7, 2018
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  13. EmAitch

    EmAitch New Member

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    Good suggestions all, thanks! Let me run this by y’all as well: it seems to me that whatever switch or relay that controls whether the engine idles, or shuts down is malfunctioning. I know there are several factors that decide that, but ultimately, once the ECM makes that decision, it cuts power to the ignition right? When it’s idling rough, I can push the pedal just a little, and it clears right up. Also, when a/c is on, it usually idles fine. With the new cat, acceleration is better than ever (I bought from original owner at 93k. Original battery pack). Which also improved battery life, I guess it was putting extra strain on battery pack, with lowered engine output. I’d like to replace this component prior to taking my to the shop, as an experiment, but I can’t figure out what/where that part is! Any suggestions along those lines?
     
    #13 EmAitch, May 18, 2018
  14. EmAitch

    EmAitch New Member

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    I never have, don’t know about the original owner, but my impression is that they took very good care of it.

    Yes

    Original battery pack. Replaced both cats with one...thinking that might’ve been bad idea.
     
    #14 EmAitch, May 18, 2018
    Last edited by a moderator: May 18, 2018
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  15. EmAitch

    EmAitch New Member

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    It just occurred to me that the problem got worse after replacing the cat. Could the fact that there is only one now, when it came with two, be a factor?
     
    #15 EmAitch, May 18, 2018
  16. audiodave

    audiodave Active Member

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    Everything else is stock on the exhaust? It shouldn't be a issue. Idle rough charging the battery? It loads the motor up.

    Posted via the PriusChat mobile app.
     
    #16 audiodave, May 18, 2018
  17. EmAitch

    EmAitch New Member

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    #17 EmAitch, May 18, 2018
  18. EmAitch

    EmAitch New Member

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    Exhaust pipe in place of second cat. Yes, rough idle during battery chg, however, smooths out if a/c on too.
     
    #18 EmAitch, May 18, 2018
  19. padroo

    padroo Senior Member

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    Was there a downstream O2 sensor? If so what happened to it?
     
    #19 padroo, May 18, 2018
  20. audiodave

    audiodave Active Member

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    #20 audiodave, May 18, 2018
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