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Rough Idle After Spirited Driving

JudderMan Mar 9, 2013

  1. JudderMan

    JudderMan Well-Known Member

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    From my previous post http://www.audi-sport.net/vb/a3-s3-forum-8l-chassis/178453-not-idling-properly-fluctuating-idle.html this is the same problem but different. Plus, that thread has gone off on a tangent.......let me explain...the above problem was cured from doing the N249 delete. It's come back now but not from normal driving only very fast driving then come to idle it's rough as hell, but not all the time.

    The idle is really rough. I get random misfires so it's not just one cylinder. I was thinking coilpacks or the spark plugs are duff? Is there a way of testing/checking the coilpacks? I don't want to have to buy them if it's not that.

    There is still the possibility of a vac leak but how do you test for it if it only happens after driving quickly. When I say quickly I mean accelerating hard onto motorways. It's not noticeable at cruising speed ie. 70mph once I've joined the motorway but when it comes to slowing down it's just at idle.

    Bit stumped really.
     
  2. badger5

    badger5 www.badger5.co.uk Site Sponsor

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    vac leak my guess
     
  3. s33nyboy12

    s33nyboy12 Well-Known Member

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    I would of said minor vac leak too.

    Sean
     
  4. JudderMan

    JudderMan Well-Known Member

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    OK thanks guys. Any ideas on where or how to test it? AFAIK vac pipes were brand new in September (previous owner bent over and got them from Audi). Could it be some vac pipes are collapsing when it's being driven fast? Just done 30 miles at sedate speeds today and not a hint of stutter. I'm sure that if I gave it the beans it would do it again like it did last night.

    Hate intermittent problems grr..
     
  5. JudderMan

    JudderMan Well-Known Member

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    Any ideas of where or how to test for vac leaks? I'm still getting this and it's started doing it when I start up. I always tend to wait until the cold start idle returns to normal ie. 1200rpm to 850rpm, but I was in a hurry the other day and tried to move it while it was still on cold start and the idle started being rough as hell, in fact it was almost dying and wouldn't move. Left it until the idle dropped then it was fine. Once I get it going and don't drive fast then it's absolutely spot on, no problems whatsoever. MPG is as you can see by Fuelly below is pretty amazing and shows that I drive slowly but that's not what I want from this car...

    Changed spark plugs again yesterday just in case and the old ones were fine, and made no difference to this idle problem. I did notice a very slight bit of oil on the rim of the spark plugs (underside part in the engine) on all four.

    So, in short, vac leaks; where, what, how?
     
  6. JudderMan

    JudderMan Well-Known Member

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    This is pissing me off now. Looks like the pipes going to the DV and a lambda sensor. I assume Bosch is the one to go for Lambdas? Is B1S1 before the cat? I need to fit my decat anyway so I'll do this at the same time.

    Only updating this for others that search.
     
  7. mitch18

    mitch18 New Member

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    Ill be keeping a close eye on this thread because mine is the exact same and really annoyong me now! Iv just changed spark plugs and still the same! Is it possible to be the SAI? Im going 2 check my pre cat lambda as well as mentioned on my thread.
     
  8. JudderMan

    JudderMan Well-Known Member

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    I have no idea about the SAI. My VCDS codes haven't flagged it up but will check again in the morning. Will report back when I have a tinker tomorrow.
     
  9. jezzy

    jezzy Member

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    Hi

    I think i posted about my lambada sensor being loose.
    Anyway the rough idling and cutting out came back after a couple of days
    The lambada sensor was fine, so i checked my hoses.
    The intercooler hose to charge pipe was split inside, i bodged the hose with some tape and its been fine now for a few days.
    Although the replacement hoses are a rip off (£150 for two hoses), i sourced some for £70 and just waiting for them to turn up.
     
  10. JudderMan

    JudderMan Well-Known Member

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    Cheers, I'll check mine tomorrow.
     
  11. Dani_B19

    Dani_B19 Audi-sports own special child.

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    MTe ive got a similar issue but my cars fine until warm, then itll drop to 400rpm when coming out of gear, it wont stall but tries to, ****s me off, theirs no vac leaks etc so dont what it is, got rid of fhe sai and the pcv system, btw my cars a s3.
     
  12. badger5

    badger5 www.badger5.co.uk Site Sponsor

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    have you had it smoke tested to confirm no leaks?
    throttle body clean and reset tried?
     
  13. Dani_B19

    Dani_B19 Audi-sports own special child.

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    No bill but theirs hardly anything to leak. The entire pcv systems gone and vents to atmos. I did the vagcom test with checkinh fuel trims and from memory they were within toleranes.

    TB wise, it did it with the standard s3 one and now the v6 one, both were/have been cleaned and aligned.
     
  14. JudderMan

    JudderMan Well-Known Member

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    Just unplugged the MAF and it's that. Idles fine, works fine, no lumpy idle. Need to get a new one then :)
     

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