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A4 1.9TDI - intermittent loss of power

Discussion in 'A4/S4 forum(B5 Chassis)' started by chuffy, Jan 7, 2008.

  1. chuffy
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    chuffy New Member

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    [Jan 7, 2008]
    Hi fellow Audi fans, I hope someone out there can help with my power problem.

    I am the proud owner of a '78 A4 Avant 1.9TDI Quattro which to date at 137k has been faultless - full Audi service history. However, recently the car has started to lose power intermittently whilst driving. The engine is fine and then all of a sudden, you put your foot down and nothing, the car will barely rev above 3000 (dangerous if overtaking). If I stop, switch off the engine and re-start it is fine again.

    The fault seems to occur after a period of idling, ie traffic or coasting down a long hill, its fine for the next mile say and then it dies.

    I have replaced the air flow sensor (£80) and this has made no difference.

    I would be grateful if anyone has any suggestions, before I end up paying silly money to the Audi dealer to try and find the fault.

    Thanks Chuffy
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  3. tubtub
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    tubtub Member

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    [Jan 8, 2008]
    I had exactly the same problem a few weeks back with my 2001 TDI. It was due a faulty N75 valve which cost £28 (I think) at a dealership. I also had them fit it, car is completely cured now.
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  4. chuffy
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    chuffy New Member

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    [Jan 17, 2008]
    Thanks tubtub for your suggestion.

    So far I have changed the airflow sensor £75.20 audi part DIY - no different.
    Audi dealer diagnosed manifold air pressure sensor, fited by them £143.66 - no different.

    As you can imagine I am becoming very frustrated as well a s skint !

    I will suggest the N75 valve to my dealer, what is it exactly? It does seeem like the tail wagging the dog - I thought Audi were good !!!!
    #3
  5. moschino
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    moschino Member

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    [Jan 18, 2008]
    It might be your CAT.
    Did you notice any strange rattles at idle coming from the engine bay over the last couple of Months?
    I had the same problem with my car, MAF ok etc... Turned out to be the inside of the CAT breaking up and blocking the exhaust causing poor performance.
    If so then you can remove the CAT and bang out the inside until clear. Stick the CAT back on, no need to replace, its not a MOT failure not to have a CAT.
    Just a thought before you start to spend more money at the dealers.
    Jim.
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