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rough idle

Discussion in 'A4/S4 forum(B5 Chassis)' started by simon1303, Apr 10, 2010.

  1. simon1303
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    simon1303 Member

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    just got back from having my 1996 t sport MOT'd and now is idling really bad, sounds a little like a subaru. but ive got no engine warning lights

    is there anything simple i can check? i havent got Vagcom
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  2. olds_kool
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    olds_kool Active Member

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    is it noisy (tappety) or eratic up and down or high
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  3. simon1303
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    simon1303 Member

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    bit more investigating carried out. its running on 3 cylinders, got no spark on no2 cylinder. ive swapped the coil packs and plugs around and they work in other cylinders. ive been told it could be the am amplifier not sending a spark to no2 cylinder. ive got it being checked early next week by someone with vag com so guess i will just have to wait till then
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  4. Geeman
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    Geeman Low Life

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    That sucks.

    At least you've got the problem identified though.
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  5. simon1303
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    simon1303 Member

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    bit more digging on the interweb and it looks like the n122 module that sits on the air box. apparantly looking at around £100 for a new one!
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  6. Geeman
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    Geeman Low Life

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    Think you might be right...! I quote from another forum...

    It turned out to be the ICM (Ignition Control Module). I had gone the route of swapping coils, plugs etc and it still kept missing on plug 3.

    You can do a quick test with a digital meter on the ICM (housed on top of the
    air intake[​IMG], front left hand side of engine bay). It has 5 pins on the incoming side and 4 on the outgoing. All it really does is switch, via some transistors, the feed to each coil.

    Set the meter to Diode test.
    On the 5 pin side of the unit the middle pin is the common emitter for all 4 transistors. Each one of the other pins is the base for of each corresponding transistor - you should get around 0.6 - 0.8v between each base and ground & also between each base and collector (the output pins). Use the negative lead of the meter on the middle pin.

    If its the ICM that's gone you will see a reading on 3 of the 4 output pins (this is what causes it to miss on one plug.

    Part numbers are:
    Bosch 4D0905351 ICM
    OEM F2045=-86642

    Do a search as there is a big difference in price, real part can cost a few hundred, unknown make around one hundred.
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  7. Geeman
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    Geeman Low Life

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    I'm sure you'll source one from a breakers yard though for a fraction of the price of a new one... just take your tester with you to check before buying!
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  8. olds_kool
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    olds_kool Active Member

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    whats the part number, ive got one from a 99 1.8t
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  9. mwarrey
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    mwarrey Member

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  10. Geeman
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    Geeman Low Life

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    Is this the thing that looks like a heat sink that sits in the top of the airbox...?
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  11. simon1303
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    simon1303 Member

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    all fixed. ICM replaced and now back on 4 cylinders. been driving the wifes seat arosa diesel to work for the last couple of days, going to be lovely to have the audi back :)
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