Poor 80-120 kmh acceleration

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by kisp113, May 18, 2026 at 8:53 AM.

  1. kisp113

    kisp113 New Member

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    Hi folks,

    I’m new to posting here, although I’ve been reading the forum ever since I bought the car — almost 7 years ago, with about 200k km driven during that time.

    Recently, I drove another Gen 2 Prius and noticed a clear difference in performance, so I started investigating mine.
    (Gen 2, 2007, currently at 390k km)

    Initially, I measured 11 seconds for 80–120 km/h acceleration, which was disappointing compared to two other Prius 2s that could do it in under 9 seconds quite easily.

    At first, I noticed that the HV battery, despite showing no fault codes, was running a bit warm and dropping below 6.5V per blade under heavy acceleration. Fair enough — it’s 19 years old. I replaced it with a newer healthy pack from 2020.

    Now the battery readings look fine, but the symptom remains:
    During an 80–120 km/h pull, the car starts accelerating well, then the ICE revs up to around 5000 rpm, and at that point the acceleration actually DECREASES. It feels like the ICE is missing 10–15 hp somewhere.

    What I found so far:

    • MAF reaches a maximum of 56 g/s — isn’t that a bit low?
    • LTFT is between 3–4%
    • MG1/MG2 and inverter temperatures are normal
    • Cat converter temp sensor 1 reads 600–800°C, while sensor 2 is 100–200°C lower. Could this indicate something suspicious?
      (The cat is aftermarket, about 150k km old. I previously had a P0420 efficiency code, which I “solved” using a spacer.)
    Thanks for any thoughts or ideas!
     
    #1 kisp113, May 18, 2026 at 8:53 AM
  2. PriusCamper

    PriusCamper Senior Member

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    Could be the fact your engine is worn out after all those miles, maybe previous owner didn't change oil often? Could also be you bought the wrong type of tires and low tire pressure.

    Can you explain the servicing you've done? When were the spark plugs replaced? What kind of oil and how often do you relace it. Throttle body and MAF cleaning? What's your MPG / KMPL?

    Also, have you considered that if you're driving up to 5000rpm you're pushing the car way beyond its limits and over the course of 200,000 Kilometers with that type of driving style you've damaged your engine? I've driven more than 300K kilometers in my Prius and can count on one hand the amount of times I've spun it up past 5000rpm.

    I mean you say you're over revving your engine and noticing a loss in power (obviously) and because of that abuse it sounds like it's time for a new Prius or new engine that you don't abuse... As in the slow driving old lady Priuses I take care of never have these problems when I drive them agressively.
     
    #2 PriusCamper, May 18, 2026 at 3:01 PM
  3. saneesh8

    saneesh8 Member

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    Do a fuel system cleanup/ throttle body/ air filter replacement. Does it feel like cutting out at high rpm? Any oil burning?

    Also just like PriusCamper suggested, plugs are good?

    Since you already replaced the cat converter, it can't be. There is no code also right?
     
    #3 saneesh8, May 18, 2026 at 4:43 PM
  4. Brian1954

    Brian1954 Senior Member

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    How much oil does your car burn?

    My guess is a bad cat. It may be partially blocked. Disconnect the front of the cat and take it for a drive to see how it responds.

    There was a recent thread created by another forum member who found out that he had a clogged cat. If interested, look at the thread https://priuschat.com/index.php?posts/3606706
     
    #4 Brian1954, May 18, 2026 at 6:01 PM
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