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Idle misfire

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by Paranoid69, Oct 9, 2013.

  1. Paranoid69
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    Paranoid69 Member

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    For a while my 2.0tfsi q avant has been running a little lumpy on idle, once you get your foot down and moving its good, and once it warms up it'll idle ok.
    Then it's started getting a little worse, wasn't throwing any codes but the other day while running I got the engine light and it registered a misfire on 4 as well as a misfire on all cylinders.
    Recommendation was to change the coils and plugs, which I've done and it's made no difference.
    If anyone's got any ideas what to look at next I'd be very interested to hear.
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  2. Big Al
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    Big Al A4 2.0T FSI Quattro

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    Check the condition of your MAF, if dirty replace. Try replacing the impulse sensor? Situated just down & back from oil cooler & oil filter on rhs of bay. That helped mine. Also I recommend changing the PRV valve (if old) and gasket on rocker cover. See my build thread for details, part numbers & costs.
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  3. Paranoid69
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    Paranoid69 Member

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    Thanks for the pointers, I'll get in there and check things out. The MAF is operating according to obdii diags but no idea what state it's in.
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  4. Paranoid69
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    Paranoid69 Member

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    Ok, been a while but have been through and had all the sensors checked, compression checked, had the induction chemically cleaned, all no improvement.
    However...
    The cars been sitting idle a lot of the time recently, to the point the battery has run flat twice.
    First time I jump started the car and for a whole it was aweful, sounded like a tractor, obviously running on less than 4 cylinders. Once it ran for a while and warmed up, after switching off and starting it up again, it got better, back to the 'normal' misfire.
    Next time it ran flat I put the car in charge and started it up the next day from cold. It ran like it would generally do from warm, still hear the misfire but pretty good really.

    So now I'm thinking alternator, ignition loom?

    Any thoughts?
    #4
  5. bez101
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    bez101 Yorkshire & Humber Rep. Regional Rep

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    clean TB ?
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  6. lynallbel
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    lynallbel Active Member

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    Whats the alternator putting out?
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  7. rizzini7
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    rizzini7 Active Member

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    Hi mate, had similar issue on mine. Don't quote me on this as mines a v6 and chain drive. So may not apply to yours
    But turned out to be a duff cam adjustment valve on mine. Car would run rough occasionally and register misfires. Mine was doing it mainly from cold start after 5 minutes or so.
    #7

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