Running Rough at idle, any new ideas ???

Discussion in 'Gen 2 Prius Technical Discussion' started by HV Battery, Sep 11, 2018.

  1. HV Battery

    HV Battery New Member

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    so I have replaced the spark plugs, did the seafoam trick, cleaned air filter, cleaned throttle body & MAF sensor

    ....still runs rough & rocky on cold startup, but then clears up after a few min of driving...

    Car does not use oil, hybrid battery is strong & 12v battery is good
     
  2. bisco

    bisco cookie crumbler

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    how many miles on her?

    have you cleaned the egr circuit/intake manifold?
     
  3. bisco

    bisco cookie crumbler

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    also, do you tend to start the car and shut it down before the warmup cycle has finished?
     
  4. HV Battery

    HV Battery New Member

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    07, 180k, no mainly just drive to work & back about 25 min drive. Cold startup is rocky for the first few minutes. have not replaced the intake manny
     
  5. HV Battery

    HV Battery New Member

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    I know the 3rd gen are bad about egr buildup but didn't know if the 2gen are also

    I drove her really hard yesterday, just to show her how much I love her after the seafoam treatment...
     
  6. bisco

    bisco cookie crumbler

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    sorry, i was looking at your info thinking 2011. no egr on gen 2.
     
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  7. valde3

    valde3 Senior Member

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    Look at the misfire monitor values? If one cylinder has more misfires swap the ignition coils around.

    If you put it in neutral with cold engine running (to get true idle) does it get smoother, worse, or stay the same?
     
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  8. JC91006

    JC91006 Senior Member

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    What does it feel like when it's "rough and Rocky"?

    It shakes all the time? You should try scanning for codes
     
    #8 JC91006, Sep 12, 2018
    Last edited: Sep 12, 2018
  9. Phildo

    Phildo Member

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    Sounds like the fuel injectors need cleaning.
     
  10. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Valve tappet clearances going off is one thing that's hard on idle. Just a thought, though I believe 2nd gen are pretty reliable. And a BEAR to adjust. Maybe just checking the gaps is not that hard?
     

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  11. Rmay635703

    Rmay635703 Senior Member

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    If you aren’t afraid of replacing the fuel filter add a dose of MMO per the bottle then fill her up so you get a mix of E30-E50 gasohol.

    If your area doesn’t sell the stuff just mix in a half tank of e85

    You might surprise yourself
     
  12. SFO

    SFO Senior Member

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    Not sure that one can replace the fuel filter without replacing the whole tank.

    Am curious to know more about the half tank of e85 and any results that might produce.
     
  13. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Pretty sure it's doable. The attached excerpt from second gen manual shows complete gas tank removal and install, but in the process I believe they show the fuel pump/filter being separated.
     

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  14. AzWxGuy

    AzWxGuy Weather Guy

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    Here is a guess. To clean the throttle body you had to remove the air cleaner assembly. The junction between these two parts is a clamp, and if you don't re-tighten it there can be un-metered air entering the intake cycle. This is air that has not passed by the MAF. It will run rough until the computer adjusts the mixture. Also, you said you cleaned the MAF. Hopefully you used the specific MAF cleaner. Did you replace the spark plugs with the recommended Nippon Denso brand? As suggested above in post #7, I would investigate the spark plug coil-overs for arcing and the codes for misfires. It is unusual for the ignition system to develop an intermittent, usually only hard failure.
     
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  15. Rmay635703

    Rmay635703 Senior Member

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    E85 is less likely to produce misfire and the misfire if it does occur is less severe in excessively lean or poor compression conditions .

    MMO Covers up leaks and increases compression, it also makes the motor sound smoother.

    In cases where you will not be repairing the real engine problem the above can allow you to drive it into the ground more pleasurably. Speaking from experience driving a car with a failed engine 60,000 miles.

    The reason I put the fuel filter disclaimer is because a very old dirty gas tank will get cleaned out by ethanol and can plug the fuel filter, it’s rare but worth remembering.
     
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  16. edthefox5

    edthefox5 Senior Member

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    The g2 seems to have fuel injector issues based on how many posts about them I have seen here.

    You have Done all the best choices for a tune up so far so give the fuel injectors a look next.
     
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  17. tidesofthesky

    tidesofthesky Member

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    LOOK AT YOUR MISFIRE COUNTS!! Sorry to yell. Ha! I was dealing with a stumbling/running rough issue for 2 months with no CEL and finally plugged techstream in and watched the misfire counts while the car idled. I narrowed the misfiring down to cylinder 3. Swapped the coil pack to cylinder 1 and the misfires switched to that cylinder. Replaced the coil pack for $50 and it is running like new again. If it's misfiring on all cylinders, then you could look for a more general issue like unmetered air/ bad fuel delivery etc. But I personally wasted so much time with my car parked cleaning MAF, throttle body, pulling plugs etc. I should have started with the misfire counts. If you don't have techstream, go ahead and order it. It's an invaluable tool. Here's a link- not the cheapest available. You can totally just buy the cable and download the software online, too.
     
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