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1.8t AEB poor idle problem and oil cap pressure

Discussion in 'A4/S4 forum(B5 Chassis)' started by BBSparky, Jan 18, 2010.

  1. BBSparky
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    BBSparky Amateur Spanner Monkey

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    Hi Guys,

    Looking for a bit of help here, have a problem that has developed on the car and just trying to work out what it could be. The car is a 98 Audi A4 1.8T (Auto) with an AEB engine and just over 100k and for the last few days it seems to have developed trouble with its idle. It seems to drop to about 400 rpm and then raise it self back up slowly to normal. Has also stalled a couple of times. I also noticed that i seem to be getting quite a bit of pressure under the oil cap ( if i leave it undone it actually rattles). Car was serviced this weekend which seems to have made it run smoother but hasnt fixed this issue. From doing a little bit of research im leaning towards the PCV being duff but wondering how i can tell for sure? I would plug in my Vagcom but my lead seems to have died which is typical!

    Cheers for any help guys
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  2. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Mine was doing exactly that just recently and it turned out to be the tank vent valve. On first start the revs would bounce from 4-500 up to 1200 and back a few times, then when driving up to roundabouts and suchlike on the overrun it would dip right down to 4-500rpm, and sit there until you came to a stop, at which point it would slowly climb back to normal.

    No guarantee, i luckily had a spare so just swapped it in.

    Mine also didnt show anything on vagcom.
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  3. BBSparky
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    BBSparky Amateur Spanner Monkey

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    Cheers Aragon, did you have the pressure under the oil cap too? just wondering if i maybe have more than one problem here :(
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  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    nah, but i didnt check, and tbh the engines done 195k so i would expect a lot of blowby anyway due to wear.

    I'd do a vagcom scan before starting to randomly swap parts as a matter of course.
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  5. BBSparky
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    BBSparky Amateur Spanner Monkey

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    Cool cheers, managed to get my lead working in the end last night after lots of messing around and had no errors at all which was actually a disappointment :(

    Dont suppose you have a part number for that valve do you? is it an audi dealer only part? also where about on the car is it so i can maybe check?

    Cheers and sorry for being a pain :D
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    It will be a dealer only part, but its fitted to all sorts.

    PN of the one i removed is 058133459 (well thats the part number on the jacket, the valve itself is 058133517)

    No idea what i replaced it with, i think it might have been from the V8 or something, because it had a funny metal bracket that the A4 one doesnt have.
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  7. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    also, it sits up on top of the air filter, underneath the silly plastic cover.
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  8. BBSparky
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    BBSparky Amateur Spanner Monkey

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    AHHHHHHHH wonder if that may explain all the clicking that was coming from the airbox area when i was having a look last night then. Couldnt pinpoint it exactly as it was very dark and my torch was very much like a candle! :)

    Cheers for the help and if your ever this way then pintage is definately deserved
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