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(solved)Fault: idle rpm jitters between ~1k-2k

Discussion in 'Automotive Electronics' started by fezder, May 12, 2015.

  1. fezder

    fezder Well-Known Member

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    So, fault is pretty easy to describe, idle rpm jitters between ~1k-2k region.
    Sometimes, it stays bit longer in higher rpm, then drops to low rpm.
    Sometimes also, i start engine, runs smoothly, in fact, very long time, if i don't start actaully driving. If i move an inch/give gas, fault comes back.
    And for note, if i free-roll car with low gear, say, first, give car none gas, ''let it go by it's own power'' car takes more speed, then de-accelerate (sorry, can't remember the right term...)
    I'we taken MAF completely off, engine runs while better, then starts to ''choke''.
    Maf was replaced while ago.
    I don't know what info i can give, but i'll answer any questions you throw at me!
    Car is lada 110 STW, so 'prolly pretty unknown for people outside of finland. Oh, and local car-club, so to say, is next to helpless....
     
  2. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Sounds like and air leak / loss.. How is the brake vacuum?? If you pump the brake when you are at 1~2k RPM, it should lower the revs.... Most engines have a low end torque vs high end power going on... If the car was designed for low end torque then the airflow under 3k is critical.... Leaky bypass hoses are usually the culprit... But I have seen many brake vacuum reservoirs that leak... Also check hoses that rub on the inlet manifold..

    If it turns out that airflow isn't the problem... Take a look at the pot on the end of the accelerator cable (if it still has one.. Can't remember its name..)

    Just looked it up TPS sensor (throttle position sensor).... Also there could be an issue with the temp sensor......
     
  3. fezder

    fezder Well-Known Member

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    woa, thanks for quick reply! too bad i can't, or at least don't intent to test today, but i'll test that brake pumping tomorrow. I'll take a video clip too to more tell about the problem in detail...
     
  4. dave

    Dave New Member

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  5. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Sorry!! I was a VW Audi mechanic for some years.... I have seen numerous faults...

    What you are describing could be a whole host of different things...
     
  6. fezder

    fezder Well-Known Member

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    nothing to worry about, you should at least then have knowledge :D
     
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I have no idea of the technology used in the car, but IF the car has an IAC (Idle Air Control) then that's a real prime suspect. These are used in cars that have throttle body injection systems. Kinda annoying.

    I did have an MAF problem that was caused by a BAD MAF where the car would barely stay running, I disconnected the MAF and the problem went away. The MAF was replaced under warranty. It happened with a fews days of the replacement.

    Back in the day of carburated engines, I had an issue where if the car was turned off within a certain amount of driving time and then the car sat for a certain time and was restarted, the idle was very rough. This turned out to be a bad solenoid valve that enabled the EGR valve. On power down, the EGR was totally on, which prevented dieseling. The vacuum solenoid valve was mounted where it would get too hot.
     
  8. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I loved my Audi 5000 CD turbo and Customer service but could not afford the maintenance costs after 10yrs e.g. hydraulic rack N pinion $2k shocks $1k.. Good thing, it got written off.

    Does your Lada have a
    LADA Idle Air Control valve 2112-1148300

    I feel empathy for any LADA owner, I once had a 63 MGB

    If it had a kitchen sink, I would have replaced it.
     
    Last edited: May 12, 2015
  9. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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  10. fezder

    fezder Well-Known Member

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    Yup guys, it does have one of those, right next to...throttle position sensor, sorry, used translator as i didn't know that part in english
    But, IAC has been also replaced once, one of the windings was broken. It's stepper motor, so luckily that's somewhat easy to test. But, mind you, i haven't tested that out, or oiled it's shaft, will do that next time
     
  11. fezder

    fezder Well-Known Member

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    okay guys, took a couple video clips, gonna upload them to youtube. Ian, brake pumbing did have effect, not shown in videa at first: when i pump fast, rpm seems to stall, or more to say, stays at 1k. you'll see for yourself in a moment
     
  12. fezder

    fezder Well-Known Member

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    i'll upload them in the order they are ready....
     
  13. fezder

    fezder Well-Known Member

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  14. fezder

    fezder Well-Known Member

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  15. fezder

    fezder Well-Known Member

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  16. fezder

    fezder Well-Known Member

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  17. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Definitely mixture related.... The oxygen sensor is going mad!!

    When you pump the brake it stabilizes a bit.... There MUST be an air leak..
     
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  18. fezder

    fezder Well-Known Member

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    wohoo, that is one the few parts that haven't been changed yet :D...
    is it lampda-sensor btw?
     
  19. fezder

    fezder Well-Known Member

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    oh, and in case someone wonders, i disabled comments due the fact many many people hate or have wrong experience with these cars, so this way it's much easier to keep comments section clean of irrelevant stuff....
     
  20. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    What happens if you disconnect the IAC?
     
  21. fezder

    fezder Well-Known Member

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    hmm, good question, worth a try no?
     

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