2008 Prius: engine idling a bit high: solutions anyone?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by timespell, Mar 17, 2020.

  1. timespell

    timespell Member

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    OK, here is the deal. I decided to clean my throttle and my MAF sensor. Also cleaned the air box and installed a new air filter about a month ago. I recently started experiencing a bit of a high idle. Its steady, so don't believe its a ignition coil problem or a spark plug as I just changed them a few weeks ago. I was thinking maybe a vacuum leak. I do have a couple of spare MAF sensors pulled out of a pick and pull junk yard.

    One possibility is maybe the air cleaner where it connects to the throttle body. When changing my plugs, When I pulled the #1 plug, it was totally saturated with oil. Like I took it and dunked it in a container full of oil. It turned out that I had bad valve cover gasket and the gasket tear was right at the corner of the #1 plug. When my mechanic took the valve cover off, you could see the gasket came apart there. Installed a new gasket took care of that. But when he replaced the air box, possible he did not put it in tight.

    So I will check that, and also give the throttle another cleaning, and put in one of my spare MAF sensors.

    Any more suggestions are welcome!
     
  2. valde3

    valde3 Senior Member

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    Prius only idles for a short time (and only when stationary) when going from stage 3 to 4 and that only happens once per drive so are you even talking about idle? If ECU is not satisfied with idle (including idle speed) this will take longer as engine will just idle until the ECU is satisfied and only then will it shut down (or if you start moving it will go back to stage 3). The Five Stages of Prius Hybrid Operation | PriusChat

    So after the engine has warmed up if you stop and engine is idling does it stop? Does it take long before it stop? If it does it could be a vacuum leak but it can also be a throttle sticking and/or ecu trying to re-learn the position.

    Times when engine seems to idle it can be spun around by MG1 and not burning any fuel at all or just using the fuel to heat up the catalytic converter. Or engine could be charging up the battery using MG1 as generator.

    If your not talking about actual idle it can be something totally different and not related to engine at al.

    It can't be caused by leak between throttle body and air cleaner as there's no vacuum there.

    One thing that you can do is reset the ECU after throttle body cleaning. Also just reading the fault codes might give you some information.
     
    #2 valde3, Mar 17, 2020
    Last edited: Mar 17, 2020
  3. timespell

    timespell Member

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    When I stop or start up, the idle seems a bit high and doesn't go down. I will work on the MAF sensor, reclean the throttle and make sure the air box is secured! And reset the ECU by disconnecting the battery ground, wait about ten minutes and see what happens. Your advice is appreciated! Thanks :)
     
  4. sam spade 2

    sam spade 2 Senior Member

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    Some owners with older models have reported that the engine seems to run longer and a bit faster right before they get an indication of a failing HV battery.

    Trying to "fix" it might be a mistake.
    If there really is a problem brewing, some lights will come on before too long.
     
  5. fotomoto

    fotomoto Senior Member

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    Is this vehicle new to you? Is the battery original or a rebuilt? If so, this might be a sign of a weak HV battery. As said, it doesn't typically "idle" like non-hybrids.
     
  6. timespell

    timespell Member

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    The idle is not terribly high, but for me higher then usual. I cleaned the throttle and threw in one of my spare MAF sensors, and tightened everything snug. Then disconnected the battery ground for about 10 minutes. But same thing--sigh! And no check engine light at all. As for the battery, probably the original one, but it seems to be OK. My only problem with the charge going down is traveling up steep hills. But then it charges up fairly quickly to 8 pars or higher!
     
  7. fotomoto

    fotomoto Senior Member

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    Double check all work for air leak(s) downstream of MAF.

    Monitor HV battery more closely (get Dr. Prius app or similar if you haven't).
     
  8. valde3

    valde3 Senior Member

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    Has it always been like this? It's kind of hard to know if this is normal as I don't know how steep or long the hills are and how fast the battery level goes down and up. What do you mean by higher than 8? 8 is maximum.
     
  9. timespell

    timespell Member

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    8 bars and higher to green max! the hill is steep and about a mile up to the top. In cold weather it only goes down a few bars, but in the hotter summer it can go down to a single bar. But once I hit a level road or down hill it fairly quickly goes up to usually green max. It is the original battery. seems to be OK.
     
  10. timespell

    timespell Member

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    car is not throwing any codes and no red triangle of death. Only code showing was P0420 which the new cat took care of.
     
  11. sam spade 2

    sam spade 2 Senior Member

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    Famous last words.
    You really have no "easy" way to actually know if it is OK or not.
     
  12. edthefox5

    edthefox5 Senior Member

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    There is a 10 MM throat clamp under the air cleaner box that seals the air box to the throttle body.

    Its not the maf stop messing with that. If the maf had a problem the engine will be stumbling and poor running and throw a code.

    High idle in a G2 with engine running good may be a starting to get old hybrid battery as others have said. Hybrid battery very suspect at that age. But hard to tell as you never posted miles on the car.

    Best way to test the hybrid battery is to do a test drive. Find a nice flat no traffic straight highway about 4 miles long. Get the car up to 60 miles an hour and set the cruise control. Turn off the ac and lights. Reset the consumption meter reset button and zero out accrued mpgs.
    We want fresh mpg data.

    Drive for about 3 miles on CC. You should see at least 55 mpg's at the end of that 3 miles.
     
  13. timespell

    timespell Member

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    No Check engine light anymore since the new cat was installed. I did everything else possible before replacing the cat and the P0420 code kept coming back on. Got about 700 miles now on the cat and no check engine light. So, yes IMO the cat I had must have been bad! And of course that cat had over 220,000 miles on it.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    My comment was aimed ONLY at the statement that was quoted.
    You are just assuming that your battery is OK without any real evidence.
    If it is the original, your assumption likely will not hold up much longer.
     
  15. prius_deep

    prius_deep Member

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    if your throttle and or maf sensor were really dirty THIS IS NORMAL your prius computer will recalibrate the -new air / fuel mixture- give it a week of normal daily driving and your idle will return to 'normal'.

    or unplug the 12v battery. I say let the car do it's job - recalibrate the new air / fuel mixture.
     
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  16. edthefox5

    edthefox5 Senior Member

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    Had my car 12 + years never cleaned the maf. Engine runs great. Maf lives in a nice world it sees fresh air post air filter. Prius emissions is highly monitored as most modern cars anything that changes its air map will throw a code.
    The engine does not have a high idle if the maf is dirty. It will have no idea how much air is coming in throw a code and the engine will be very unhappy.

    Leave the maf alone. If you want to spray some maf cleaner on it good for you but most likely it’s just going through it’s various stages of warm up. Mine has done that since I bought it new.

    It’s either that or the hybrid battery is constantly low charge. Mine did fast idle all the time when my battery started to fail. After a Prolong intervention it no longer fast idles,
     
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  17. prius_deep

    prius_deep Member

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    if your throttle and or maf sensor were really dirty and you timespell cleaned it/them THIS IS NORMAL your prius computer will recalibrate the -new air / fuel mixture- give it a week of normal daily driving and your idle will return to 'normal' before the week is up; the longer trips you take, the more data your prius will have to recalibrate to the -new air / fuel mixture-. If you did a good cleaning job, your prius is getting more air.

    it will recalibrate!
     
  18. timespell

    timespell Member

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    I had two spare MAFs that i picked from pick/pull. So I cleaned both with MAF cleaner and stored both. So I replaced the original with one of the spares, cleaned the original which was pretty dirty, and stored that away. And also the throttle was pretty dirty. So I cleaned the throttle, air box, and installed a new air filter. I installed new Denso spark plugs but decided against the SK16R11 long life, in favor of the Iridium IK16TT Twin tip plugs. Replaced both the upstream air/fuel sensor and downstream o2 sensor. But could not get rid of the shitty P0420 code. Finally opted out for a new aftermarket Cat. from First Choice Exhaust out of Canada. Was a very easy install. I reset the CEL and almost 900 miles later and still no more P0420 code. Very happy with the results. NY State has adopted the same emissions laws as California's clean air act. Which doesn't allow after market cats to be sold or used. And most after market cat companies will not ship aftermarket cats to either state. So was surprised when they shipped me the cat with no questions asked. Cat has a 5-year warranty and gets great mostly 5-star reviews.

    On another note, had to replace the valve cover gasket which was leaking internally near the #4 cylinder where the plug was saturated with oil. The gasket was torn in that area. New gasket solved that problem. I only use full synthetic oil and it showed with the valve cover removed! Was really clean--like a light bronze. I use Walmart brand Super Tech 5W-30 High Mileage oil for engines over 75,000 miles (cost only $14.88 per 5 QT container). I also use Fram Pro Synthetic FPS4967 oil filter (6 for $28 with free shipping on ebay).

    Right now I am getting only 37 to 40 MPG, which is affected by cold weather in my area (Central NY) and snow tires. With my snow tires off and the weather starting to warm up, new cat and such, I expect to be back to my normal 44-48 MPG in a month or so--hopefully!

    By the way, thanks for your helpful input! :)
     
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  19. sam spade 2

    sam spade 2 Senior Member

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    Other exhaust components can be tested and certified for use in tight air standard states.
    So it is possible that the CATs can too.

    But I think it is much more likely that the difference is that it came from Canada.......where the US EPA has no jurisdiction.
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

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    If unusually high idle speed still is a problem, check for an air leak downstream from the mass air flow sensor. For example, the clamp holding the air cleaner housing to the throttle body, the gasket between the throttle body and the intake manifold, a loose PCV hose, etc.
     
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