S3 205 GTI - Everchanging Idle Speed
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  1. #1
    1000+ Posts Andrew Ch's Avatar
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    Default S3 205 GTI - Everchanging Idle Speed

    Hoping the brains trust can help. The idle on my car keeps changing and I don't know why. Car is running great, nice and strong but lately the idle climbs 100 - 200 revs from normal when warm and then this becomes the set idle from then on.

    When this happens engine idle is rough but runs smooth when driven. I then adjust idle screw back to 950 ish and it's okay for a while but then changes again. And the idle screw is not moving of it's own accord.

    I have good leads, dissy cap and rotor, air filter, oxy sensor, have cleaned and checked AFM, SAD and throttle body, checked air hoses and fittings. Just wonder what to check / adjust next, any suggestions greatly appreciated .....

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  2. #2
    1000+ Posts cam85's Avatar
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    Hey Andrew,

    I removed and cleaned the idle screw, made a very small but noticeable difference. It was pretty dirty. I then removed the whole throttle body and cleaned that, it was pretty dirty and clogged up. Then decided to clean the elbow before the TB and that was filthy with blow by oil etc caking up over the years. After putting that all back together the idle was pretty good and strong. Still was a little erratic and then changed the ECU temp sensor switch as I had a spare lying about and that also made everything else rock solid. My fuel economy improved to.

    Clean the idle screw first, its easy and quick to begin the elimination process. I hate trying to sort these things out.

    ( Cough...haltech...cough )

    Cam
    94 205 Gti Classic #9
    91 205 Si
    87 205 GTi Race Car
    http://www.aussiefrogs.com/forum/res...-race-car.html

  3. #3
    1000+ Posts schlitzaugen's Avatar
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    I don't worry too much about that, mine does something similar. My idle is apparently stable but on the high side, perhaps a tad over 1000RPM. Can this be caused by an erroneous lambda sensor reading?
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  4. #4
    1000+ Posts Andrew Ch's Avatar
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    Have already cleaned screw and everything else is regularly maintained so nothing oily gets a chance to buildup.

    Bosch Lambda sensor is relatively new, wiring was redone with new plugs and car is going great, just not the idle.

    Meant to add sparkplugs are showing a light tan and compression is good at around 180ish on all four pots.

  5. #5
    1000+ Posts cam85's Avatar
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    ECU temp sensor switch?

    Cam
    94 205 Gti Classic #9
    91 205 Si
    87 205 GTi Race Car
    http://www.aussiefrogs.com/forum/res...-race-car.html

  6. #6
    1000+ Posts Dave's Avatar
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    You say it runs rough with the high idle. Maybe an air leak downstream of the afm therefore unmetered and running lean.

    Won't be as noticeable on throttle with less vacuum.

    Dave


  7. #7
    1000+ Posts cam85's Avatar
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    Ill second that. ALthough you may have checked, check five times. I found a couple around elbow before the throttle body where pipes loin. the little male parts that stack out can leak at their base. I sprayed some detergent on the and found them leaking.

    Cam
    94 205 Gti Classic #9
    91 205 Si
    87 205 GTi Race Car
    http://www.aussiefrogs.com/forum/res...-race-car.html

  8. #8
    1000+ Posts djvu205's Avatar
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    since removing the SAD on my car the idle has been perfect once the engine warms, when its cold it takes a little feathering of the throttle but doesnt bother me. with the sad connected it was always jumping up and down in the rev range sometimes as high as 2000 rpm without me going near the car? maybe its a faulty SAD? or as mentioned the piping in and around that area.

  9. #9
    Fellow Frogger! DjB8V's Avatar
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    Cant wait to get rid of my SAD. One less thing to worry about



    C


    205GTI - 8 valve, single cam coolness.



  10. #10
    1000+ Posts Andrew Ch's Avatar
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    Thanks for the help from all concerned. It's a good point David re: pipe after AFM will do another check on elbow pipe and fittings, then will ECU temp sensor switch and check SAD and pipework.

    In regards to Haltech, and that's a nasty cough you have Cam, I am determined to keep the car stock including ECU and SAD regardless of the odd bout of frustration.

  11. #11
    1000+ Posts cam85's Avatar
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    Good work andrew.

    Ive just finished getting a pretty sad 205 back to original spec ( mechanically/electrically...less back seats and interior ) for rego and has actually been really rewarding.

    Im envious of your current ride. It must be a wonderful daily car with character!

    Cam
    94 205 Gti Classic #9
    91 205 Si
    87 205 GTi Race Car
    http://www.aussiefrogs.com/forum/res...-race-car.html

  12. #12
    1000+ Posts Andrew Ch's Avatar
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    You're right I just love working on it and live 5 minutes away from twisty country roads that the car eats for breakfast. All great fun cheers...

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