Idle rev go up and down continuously

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Artunc, May 7, 2026 at 5:29 PM.

  1. Artunc

    Artunc New Member

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    I tried to search the site but couldn’t locate any discussion about my problem. My 2011 Prius just started to rev up and down shortly after oil change. The coolant is a little low too. The codes it shows are P0171 and P0401. I checked for vacuum leaks but nothing I can see. The EGR assembly and intake manifold cleaned a couple months ago. When I put it to Maintenance mode, it rough idled and died throwing errors P0102 P0113 and saying check hybrid system.

    I would appreciate if anyone can point me to right direction to troubleshoot this issue.

    Thank you.
     
    #1 Artunc, May 7, 2026 at 5:29 PM
  2. Brian1954

    Brian1954 Senior Member

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    What scanner are you using to check for trouble codes? Does the scanner read live data? If so, what are the short-term and long-term fuel trims?

    An engine that revs up and down during idle sounds like a vacuum leak to me. The P0171 code confirms that the engine is running lean.

    My guess is a problem when you cleaned the EGR system a couple of months ago. Did you use new gaskets between the intake manifold and the cylinder head and also between the EGR pipe and intake manifold when you put it back together?

    Did you clean the EGR cooler. The P0401 code indicates insufficient flow through the EGR circuit.
     
    #2 Brian1954, May 7, 2026 at 8:28 PM
    Last edited: May 7, 2026 at 10:22 PM
  3. PriusCamper

    PriusCamper Senior Member

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    Crappy oil change places are sometimes the last place people drive their car before its ruined. Just helped walk a friend through a major clean and high voltage battery recharge with too much oil in his Prius. So infuriating!

    In my research to help him I learned that these untrained workers often inspect the air filter for an upsell and fail to put the cover back on correctly, which can cause these symptoms.

    I also worked on 2006 Prius a while back that had these symptoms with a different error code and the fix was replacing the throttle body because the throttle body position sensor had failed.
     
    #3 PriusCamper, May 7, 2026 at 11:39 PM
    Last edited: May 7, 2026 at 11:51 PM
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  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    One possibility: did you happen to have a 12 volt battery disconnection? That'll make for surge-and-drop revs, for the next few start-ups. I'd speculate it's the car recalibrating throttle response.

    That said, all those codes, probably more to it. P0401 is for low EGR flow; this is after the EGR cleaning? You did the cleaning?

    What's the miles on it, and was that the first EGR cleaning? You mention low coolant: was that the impetus for the cleaning?

    Can you clarify the timeline? You mention 2 sets of codes, and egr/intake cleaning and an oil change, but it's not clear the order and the time between each.
     
    #4 Mendel Leisk, May 8, 2026 at 12:02 PM
    Last edited: May 8, 2026 at 12:10 PM
  5. Artunc

    Artunc New Member

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    The scanner they used was an Innova 5160rs. I used Dr Prius and Auto Doctor to read live data. It has 203.7K miles on it.

    At a cold start, long-term trim shows 0.00% and short-term trim shows 17.19%. MAF air flow rate is 6.12 g/sec. (see attached)

    I cleaned the EGR cooler, EGR valve, intake assembly 2-3 months ago and that resolved the EGR error code I was getting. (They were pretty clogged up)

    The oil change was 2 days ago, this issue started yesterday.

    After it idles for a minute or so it throws P3190 and shows check hybrid system, which I think that's a secondary code due to engine stumbles and not providing enough power to sustain power.

    Every time it throws hybrid system error, I reset the codes using the apps and disconnect the battery 5-10 minutes.

    Thanks.
     

    Attached Files:

    #5 Artunc, May 8, 2026 at 1:09 PM
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  6. Artunc

    Artunc New Member

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    I just tried to post a video and audio of the issue, but this web site doesn't allow me to upload them, saying file doesn't have allowed extension.
     
    #6 Artunc, May 8, 2026 at 1:26 PM
  7. Brian1954

    Brian1954 Senior Member

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    Try removing the mass air flow (MAF) sensor and clean it with the proper cleaner. Install it and make sure the electrical connector is attached properly.
     
    #7 Brian1954, May 8, 2026 at 5:51 PM
  8. Artunc

    Artunc New Member

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    Thanks for that suggestion. I just bought and tried a new MAF sensor from Auto Zone but that didn't make any difference.
     
    #8 Artunc, May 8, 2026 at 6:40 PM
  9. Mendel Leisk

    Mendel Leisk MMX GEN III

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    You need to upload video to YouTube, then post a link here.
     
    #9 Mendel Leisk, May 8, 2026 at 9:24 PM
  10. PriusCamper

    PriusCamper Senior Member

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    He can't post the link or pictures or videos until he has 5 comments and is no longer moderated. This is why we have so few spammers at PriusChat.
     
    #10 PriusCamper, May 8, 2026 at 9:37 PM
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  11. Brian1954

    Brian1954 Senior Member

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    I am guessing that the long-term fuel trim was 0.00% because you had disconnected the 12v battery. The car only ran for 15 seconds for the short-term fuel trim to get to 17.19%. If possible, drive the car for 5 to 10 minutes and check the fuel trims again. Stop clearing the trouble codes and disconnecting the 12v battery.

    Like PriusCamper stated in post #3, maybe the oil change place checked your air filter and didn't put it back together correctly or they knocked off a vacuum hose.
     
    #11 Brian1954, May 8, 2026 at 10:00 PM
  12. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Yeah checked, he’s currently got 4 postings, so close lol.
     
    #12 Mendel Leisk, May 9, 2026 at 9:40 AM
  13. Artunc

    Artunc New Member

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    The site still doesn't allow me to post a video link here yet because of below requirements.

    Minimum Requirements
    The number of posts you have created must exceed: 4 (Yours: 4)
    The number of days you have been registered must exceed: 1 (Yours: 1)

    Please keep replying to my post so I can get over these thresholds.

    Thank you for that tip, I checked the air filter box and its vacuum hoses; they seem fully seated and secured.

    Thanks.
     
    #13 Artunc, May 9, 2026 at 1:12 PM
  14. Artunc

    Artunc New Member

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    I took the actuator motor off the EGR valve (see attached picture), and the exposed rod/pintle in the middle is completely frozen. It won't move up and down at all.

    Has anyone had success unsticking a fully seized valve stem like this, or is the internal mechanism toast, or it that normal?

    Thanks.
     

    Attached Files:

    #14 Artunc, May 9, 2026 at 3:01 PM
  15. ASRDogman

    ASRDogman Senior Member

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    The cheap chinese ones don't work correctly. Basically, none of them do, except the oem
    from Toyota. Electrical parts like that for the Prius are best gotten from Toyota.

    If you take the valve off, you can spray it with carb cleaner, that will help free it up.
    Since you already have the cover off, you can spray around where the valve goes into the
    guide, and gentry tap it with a hammer to get it to move. More carb cleaner.... repeat until
    it moves freely...
     
    #15 ASRDogman, May 9, 2026 at 3:35 PM
  16. Artunc

    Artunc New Member

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    It was definitely the stuck EGR valve! I used some carb cleaner to finally loosen it up, and the car is running perfectly now.

    Thank you everyone for the help and advice!

    I will post a video of the issue tomorrow so anyone else has this issue can see it.

    Thanks.
     
    #16 Artunc, May 9, 2026 at 4:32 PM
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