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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    Location:
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    Vehicle:
    2011 Prius
    Model:
    III

    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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    Jan 31, 2021
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    Location:
    South Central PA, USA
    Vehicle:
    2011 Prius
    Model:
    III
    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
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