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  1. #1
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    A3 2.0 TDI Sport turbo / boost lag / delay / flat spot

    Hi there,

    Been reading these forums for a few weeks, just decided to register as I have now got an A3 2.0 TDI Sport.

    Love the car - absolutely awesome - better than my Golf 1.9 I just got rid of :D

    Anyways, basically I wondered if any of you guys could help with this.

    I've noticed that when I put my foot down there is very often a kind-of delay / lag with the boost from the Turbo.

    It's kind of like it starts to boost for a second, then goes flat for a few moments then carries on boosting. If this makes sense?

    Could it be the MAF sensor? Can this be cleaned? Or if not would you recommend a cheap-o one from eBay or the genuine Bosch one?

    Or could it be something like an injector?

    I've noticed that when starting up it puffs out what I think is probably faint blue smoke but only for a minute after starting up.

    Thanks in advance!!

    Matt

    Oh- and it's the 8P chassis - 54 reg. Thanks!

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  3. #2
    NHN
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    Welcome to the forum.

    Given the age & the symptoms, it could be a variety of things, fuel filter, maf & even turbo, has it lost power at all then you start it again & powers back?

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  4. #3
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    Hi, thanks for your reply.

    It is due for a service now - which I will do myself - just bought all the filters and decent oil. Would be nice if it was just the fuel filter which was the issue. I threw some injector cleaner in my fuel tank about a week or so ago which doesn't seem to have made any difference.

    When the gas pedal is pressed it has a 'lag' or delay or flat spot if you like for a few moments before the boost will kick in properly to drive me away. Hope this makes sense.

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    It could be the tandem pump - seal leaking oil into the fuel system. I have same symptoms as you mate puff of blue smoke on a start, black fuel in the fuel filter. Car was driving perfect for a couple of weeks after changing fuel filter but it is laggy again which makes me think it is time for a new tandem pump.
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    Thanks for that - would it be just a case of looking into the fuel filter to see if it is black fuel? Cheers!

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  8. #7
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    A3 2.0 TDI Sport turbo / boost lag / delay / flat spot

    Reach round the back of the engine (while its off) & find the turbo actuator rod which will be coming from the side of the turbo to a small actuator unit near the cylinder head. This rod should be a little stiff but not overly so & most important it should move smoothly & linear i.e. not soft then stiff then soft again etc etc.

    If the rod feels like its sticking or not moving freely, that's most likely your issue as the variable vanes won't be opening properly. Do a search for 'cleaning turbo' which should give you plenty of info on how to resolve the problem.
    TDI PD170 S-Line Sportback... 191.2bhp & 290lb/ft torque @ standard with an iffy turbo! No idea with the new one or Shark Stage 1 remap installed, DPF off Stage 1 ready to go, Suspension & wheels to be fitted!
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    Genuine S-line 18" alloys, A3 Sportback rear lights. A3 5dr window switches & mirror switch. , Brand new PD170 engine cover. PM for details.

  9. #8
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    Thanks, I already had my service stuff so yesterday I did the air & pollen filter and also the fuel filter - I also cleaned out the canister for the fuel filter. There was (some) black in there but not overly. The fuel I took out the canister was a bit dirty but I would imagine with it being a fuel filter which hasn't been changed in a year may be normal? Or am I wrong?

    And thanks Max, will also check that too. Hoping it's just something I can sort myself as I do bits and pieces myself to save money. Thanks for suggestions! Will keep you updated :D

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    If you really wanted to check the state of the fuel in lines temp, could fit some clear tubing & new filter to see what is being cycled back round, that way would determine maybe if its adding contamination.

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    A3 2.0 TDI Sport turbo / boost lag / delay / flat spot

    Quote Originally Posted by SAiLO View Post
    It could be the tandem pump - seal leaking oil into the fuel system. I have same symptoms as you mate puff of blue smoke on a start, black fuel in the fuel filter. Car was driving perfect for a couple of weeks after changing fuel filter but it is laggy again which makes me think it is time for a new tandem pump.
    When the oil gets in the fuel system does it work both ways and fuel also gets into the oil. Was worried as this would thin the oil?

  12. #11
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    Did my oil change and oil wasn't thin. There only seemed to be a little bit of oil in the fuel filter housing, however I'd prefer there wasn't of course. Did a thread about a couple of leaking boost pipes (oil leaking under neath the car from them) so could this have anything to do with the hesitation or lag on the boost sometimes when I put my foot down?
    Forgive me if I sound daft

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    I would make sure it is deffinitely oil getting into the fuel filter as in my experience these are usually black when you change them, which is why you change them. I also believe in changing them regularly as the more choked they become the less efficient they are. Black filter does not necessarily mean engine oil in the fuel though, is what I am trying to say.

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    Yeah it was perhaps just dirty - it was black which I expected, but in the fuel there was little tiny speckles of 'soot' - guess it's just the filter doing its job.

 

 

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