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Thread: very rough idle

  1. #11
    Join Date
    Nov 2004
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    now...

    i determined its not the idle control valve...
    tested a friends icv on the car and its working well...

    its also not the air flow thing...
    did the same thing...

    can a clogged catalytic converter be the cause?
    any other ideas?

    ill be doing a more thorough check of the air intake hoses
    again tom

  2. #12
    Join Date
    Oct 2006
    Location
    Reading, UK
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    Quote Originally Posted by pong
    now...

    i determined its not the idle control valve...
    tested a friends icv on the car and its working well...

    its also not the air flow thing...
    did the same thing...

    can a clogged catalytic converter be the cause?
    any other ideas?

    ill be doing a more thorough check of the air intake hoses
    again tom
    Idle bounce like you've described is almost always certainly a vaccuum leak - caused by a hose with a hairline fracture in it.

    It's bouncing because as the icv is opening, more air is being drawn through the crack in a hose (between the MAF and ICV, due to more vaccuum)- causing the icv to close again as there's now too much air. Unplug your MAF with the engine running and see if the idle stabilises - if it does it's a sure sign one of your hoses is cracked.

    If so, take all of your air hoses off the vehicle and flex/bend them around a bit - any cracks will immediately show up.
    Last edited by Ferret; 04-23-2007 at 09:07 AM.

  3. #13
    Join Date
    May 2006
    Location
    Antwerp, Belgium
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    552

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    I concur. When I had a backfire from the LPG my ICV elbow hose disconnected and I had the same thing albeit in lower RPMs but still fast hunting up and down RPM needle.
    If you do the reset and the problem is still there immediately after it's most likely vacuum leak. Sometimes it can be something real stupid once you find it but I'm pretty sure you have it.
    2008 audi A3 1.9tdi
    (former 1991 520i LPG)

  4. #14
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    Nov 2004
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    oh crap...

    i looked at the vent hose...
    05 VENT HOSE 11151708801
    i tried removing it...

    it crumbled...

    replaced it... still nothing happend...

    when its out... idle seems to be better...
    but i couldnt run bcoz the idle drops as i change the gear

    any ideas where i should look?

  5. #15
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    Nov 2004
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    205

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    now... i checked the throttle sensor...

    its really oily...

    is this probably the cause?

  6. #16
    Join Date
    Oct 2006
    Location
    Reading, UK
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    Quote Originally Posted by pong
    oh crap...

    i looked at the vent hose...
    05 VENT HOSE 11151708801
    i tried removing it...

    it crumbled...

    replaced it... still nothing happend...

    when its out... idle seems to be better...
    but i couldnt run bcoz the idle drops as i change the gear

    any ideas where i should look?
    If it's done that, it's more than likely half your other hoses are in a similar condition...

  7. #17
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    Nov 2004
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    205

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    how can u detect vacuum leaks...

    the only thing that i know i can do is to
    do it via trial and error...

    is there any other way to detect vacuum leaks?

  8. #18
    Join Date
    Mar 2007
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    13

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    Quote Originally Posted by pong
    how can u detect vacuum leaks...

    the only thing that i know i can do is to
    do it via trial and error...

    is there any other way to detect vacuum leaks?

    Figured I would throw my two cents in.
    You can spray water on all the connections with a squirt bottle. When you hit the right spot things will improve or get worse.
    if it is small enough the water will actually seal the air leak for a moment. if it is a bigger leak the water will be drawn in to the engine and cause it to run rougher. This has worked for me in the past.

  9. #19
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    Nov 2004
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    updates... i changed most of the hoses... still no change...

    when i unplug the maf...

    it stabilizes... but at 4k rpm...

    so its still a vacuum leak... d only thing that i didnt change so far
    are d hoses from maf to icv to throttle body...

    ill look at that again...

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