Monster MotorsportChris Nott
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  1. #1
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    Misfiring when revs drop

    I've just gotten this problem. Wondering if anyone has any ideas of what it could be from the symptoms.

    When I am driving for say 30mins at motorway speed, then slow down at the end of my journey where I'm either stuck in traffic or in a slow speed limit (40kph) the engine feels like it is misfiring but only on part open throttle. Not on closed throttle and not when idling.

    When this happens, if I put the foot the floor it chuckles away for a second or two, but once the revs rise it clears up and the engine is back running normally again whilst the revs are up. If I let the revs down again it will chuckle away again.

    A short bit of driving with the revs up clears up the problem altogether.

    The problem never happens when starting the car up. It only happens after driving for a period of time at above 80kph and then drop down to say 40kph or idling in traffic.

    Could this be misfiring? I replaced my spark plugs only a few months ago when it was definitely misfiring, but it was misfiring consistently when I hit high revs at high speed. So previously under normal driving the engine was running fine, but as soon as I floored it and hit high revs it would misfire.

    The engine feeling I am getting now at low revs feels like the same feeling when it was misfiring at high revs before i.e. misfiring. Could this be misfiring or something else that just seems like misfiring?

    If it is misfiring, could my spark plugs be the culprit again?

    I replaced all my coil packs about 3 years ago.

    Anyone have any instructions on how to check via vag-com if it is misfiring?
    Last edited by metricspaces; 14th December 2012 at 22:04.

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  3. #2
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    Just to note, my OBD port has fallen behind the dash, so when I get access to that again I can scan for faults, and update with what I find.

  4. #3
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    Any ideas guys?

  5. #4
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    Smile

    Bad earth???? Or coil pack !!!!!!!!scan with vcds or pull out coil packs 1 by 1 see if engine idle changes if 1 dosent least you know what cylinder it is??

  6. #5
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    Just got access to my OBD port. There's no error codes showing up in vag-com.

    The problem only happens after driving for a good period of time and then slowing down to around 40kph or idling as I sit in traffic.

    When I startup the problem is never there.

  7. #6
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    From a quick scan of other threads it seems that it's not unusual for faults not to be logged when the engine is misfiring.

    I'll hook up my VAG-COM when I get the symptoms again and see what shows up. Looks like I need to check blocks 15 & 16 http://www.ross-tech.com/vag-com/m_blocks/010-019.html

    One other thing I noticed is that I get a burning smell when the car is behaving like this.

  8. #7
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    Quote Originally Posted by metricspaces View Post
    From a quick scan of other threads it seems that it's not unusual for faults not to be logged when the engine is misfiring.

    I'll hook up my VAG-COM when I get the symptoms again and see what shows up. Looks like I need to check blocks 15 & 16 http://www.ross-tech.com/vag-com/m_blocks/010-019.html

    One other thing I noticed is that I get a burning smell when the car is behaving like this.
    What temp readings you getting inside car I dash temp bang ion dead centre 90 degrees could be a blocked cat?? Give it some welly through the gears flat out that will throw the code!! Could be cat smell when hot blocked doors you fans kick in ect when at 90 degrees?

  9. #8
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    Yep, the temperature dial on the dash board reads dead on 90.

    But I do have a problem with my cooling fan. Sometimes it does not kick in. It's a very intermittent problem. See Intermittent Problem with Cooling Fan

  10. #9
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    Quote Originally Posted by metricspaces View Post
    Yep, the temperature dial on the dash board reads dead on 90.

    But I do have a problem with my cooling fan. Sometimes it does not kick in. It's a very intermittent problem. See Intermittent Problem with Cooling Fan
    Well I'd sort that first car gets hot enough as it is without fans things will melt so it's either radiator fan switch cheapest option or mine was fan controll module underneath battery two big connectors held in with 2 10mm nuts!! Easy too replace!!

  11. #10
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    I would be pretty confident that my fan issue has nothing to do with the problem here. This problem happens when driving at slow speeds where airflow is sufficient to keep the engine temp below 90 degrees. The fans only come on at 100 degrees.

    Obviously I would like to fix the fan issue too. But it has turned out not to be as simple as you may think. See my thread, everything you could think of has already been replaced\investigated Intermittent Problem with Cooling Fan

 

 

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