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

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

  1. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Not faulty!!! The oxygen sensor is doing its job!! Because it can only move so far it cannot compensate that's why its hunting... If you pump the brake you are taking air from the system.. so there is too much air and the lambda sensor is reaching its max...
     
  2. fezder

    fezder Well-Known Member

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    oops, i misread you post, sorry

    the fact is, i'm pretty green with automotive stuff, so you guys are great help, no matter the outcome! :)
     
  3. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Probably.

    With NO brake application (as evidenced by your videos), Note

    Unusual Lurching Or Hesitation
    • An early warning signal of Lambda sensor failure in the form of an uneven idle can be noticed by a driver who feels the vehicle wanting to surge ahead when at a red light or stop sign. Or, conversely, when it is time to go, the driver feels the vehicle hesitating after the accelerator is applied.
    From this site: http://www.ehow.com/list_6005864_symptoms-faulty-lambda-sensor.html
     
    • Informative Informative x 1
  4. dave

    Dave New Member

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  5. fezder

    fezder Well-Known Member

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    took off IAC, same thing goes on, no difference with, or without it. started engine without it
     
  6. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    This also:

    "Thanks for the video. My 95 Dodge Ram was doing exactly what you described, and when I removed the electrical from the IAC, cleaned the contacts, and put it back, she runs perfectly now. Your video saved me a lot of time and money. Cheers."

    From:

    Cheaper, easier than an Oxygen Sensor replacement.
     
    • Informative Informative x 1
  7. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Odd that's there's NO reaction.

    Check and clean the IAC contacts.
     
  8. fezder

    fezder Well-Known Member

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    cleaned, nothing changed?
    i'll clean it again, perhaps i wasn't thorough enough
     
    Last edited: May 13, 2015
  9. fezder

    fezder Well-Known Member

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    okay, now there was some change: i pushed IAC gently at its smallest retraction, and idle rpm was now even 2k, in same longevity manner. And, i couldn't reset it, it stayed at it's short retraction.
    Any help? oh, and MAF was connected during this test, and turned all possible stuff on, radio etc. and it didn't have effect
     
  10. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    OK.

    Retracting the IAC emulates a slightly opened condition, which increases idle.

    From your description, the IAC mechanism (shaft) may be dirty, causing its action of less than smooth and "sticky".

    Try thoroughly cleaning the interior of the IAC (with carb cleaner or equivalent), especially around the shaft area, let dry and try again.

    While the IAC is removed, it would be worthwhile to check the resistance of the IAC coil(s). Can you do that?
     
  11. fezder

    fezder Well-Known Member

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    both were 53.8
     
  12. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    OK. Sounds very high. But, it is rare that a coil's resistance would increase and even rarer that both coils would change by an identical amount.

    Google "IAC resistance". Most are considerably less than that. Also note how relatively small variations render the device unusable.

    Are there any brands, numbers, etc. on the IAC that might lead you to its identity? And then, perhaps resistance specs?

    Did cleaning it make a difference?
     
  13. fezder

    fezder Well-Known Member

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    double checked resistance, it was correct. But, nowhere near 15 ohms google suggests as most, at least what i could find.
    only other marking is b298302, apart from russian language & 2112-1148300 code.
    couldn't find any specs for this thing....
    oh, and i'll test it in couple minutes
     
  14. fezder

    fezder Well-Known Member

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    okay, now it seems to okay, somewhat, idle is still bit high, 2k, but, afaik, it's supposed to be before IAC is in its place?
     
  15. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    OK. Although don't know any auto engine that idles at 2K RPM. More like 750 or so.

    How about idle speed after engine is at operating temp? Or with car in gear?

    Some engines systems, at cold (or initial) startup are intentionally idled UP to provide additional air to accelerate the heating of the catalytic convertor.

    Does disconnecting the IAC power change anything now?
     
  16. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The IAC is typically like a stepper motor. It could have a seal issue. Do you have a propane torch? If you do, just let some of the gas escape near potential vacuum leaks. RPM should increase a bit unless too much is added, then it will decrease. Do the injection with the IAC electrically disconnected.

    I think we can rule out the brake booster diafram. You could disconnect and plug the line. Pedal effort wil COSIDERABLY increase so be careful.

    The computer controlled engine removed a LOT of vacuum operated stuff.
     
  17. fezder

    fezder Well-Known Member

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    i test drove it, it settlted smoothly from 2k to less than 1k. so now there isn't any fault. perhaps IAC was just so dirty/corroded it couldn't move?
     
  18. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Yes. That was one of the suggested problems. Tolerances for the actuator shaft are fairly tight to avoid air leaks. Thus, a little dirt/dust can reduce response.

    Good job!
     
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  19. fezder

    fezder Well-Known Member

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    Thanks for you guys! this fault has been on/off nature for about 4 years....quite annoying
     
  20. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Glad you sorted it!!

    Too many engineers read fault codes and just replace parts.... If the sensor shows a fault, its normally due to some other problem and the sensor is simply out of tolerance...

    Well done...
     
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  21. fezder

    fezder Well-Known Member

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    i just try to do something and ask then from people who actually know something, instead of from those simply say buy that meter and so on....
    that tolerance-thing i gotta remember in the future!
     

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