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Car occasionally jerks when slowing down or accelerating slowly

Discussion in 'A4/S4 forum(B5 Chassis)' started by vesuvius, Sep 29, 2009.

  1. vesuvius
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    vesuvius New Member

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    [Sep 29, 2009]
    Hi,

    Im new to Audi, just bought an A4 1.8T B5, 1997 last three weeks. Everything was perfect after I sent it for service until last week it started to jerk.

    The problem is it jerks occasionally and its difficult for me to show the mechanic what the problem was.

    Sent the car for that fix and they first said there was a hose leak, replaced it for about 190. 5 minutes later the problem resurfaced and I came back and changed the power unit. Still not working, then they found another hose leaking i.e. they said it was the vacuum pipe.

    Thought that solved the issue but after 2 days the problem resurfaced. Any ideas?

    By the way, I sent the car to Everauto(malaysia).
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  3. vesuvius
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    vesuvius New Member

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    [Sep 29, 2009]
    Forgot to mention, Im also facing a loss of power and the acceleration isnt as smooth as before and also there's a faint smell of fuel when it jerks.

    Occasionally theres mild white smoke but the mechanic said its the turbo..is that true? Please advise. Tks.
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  4. jcb
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    jcb Active Member VCDS Map User

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    [Sep 29, 2009]
    check all vacuum pipes and also your recirc valve.

    I found I had a hesitation when going from overun to part throttle. not enough to jerk the car but noticeable.
    also noticed it when going the other way (part throttle to overun)

    swapped the OEM DV for a Forge unit and the problem went. I also swapped a number of hoses and teh intercooler so it is possible it was a vacuum/boost leak as well.
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  5. vesuvius
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    vesuvius New Member

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    [Oct 3, 2009]
    Tks jcb. Checked for leaks, non apparent ones. Below are some trials the mech did to troubleshoot:

    1.suspected it was the ignition coils. Replaced with temporary ones for trial & error. No luck, jerking still happens.
    2.cleaned the throttle body. Jerking went worse, added variables to the prob, i.e. occasional black smoke with a strong smell of fuel. - mech says the throttle body's not in good condition, but would this cause thejerking?

    Additional findings -
    Jerking occurs less when accelerating and driving at high speeds, the trigger is always deceleration and subtle changes fr low revs to high revs..

    Any idea?

    Now, the car is kind of being put on a trial run test i.e. i have to send the car back on Monday to mech and he'll change something and see whether it works..kind of a hassle..

    Additional input: the car has been running with RON97 for the past 12 years and I recently changed to RON95 due to price hike in my country's petrol. Would this have any impact?
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  6. Tavli
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    Tavli Member

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    [Dec 21, 2009]
    Mass Air Flow maybe???????????
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  7. richie_jones
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    richie_jones Member

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    [Mar 7, 2010]
    Sorry to drag this post up , but my car jerks in exactly the same way, when decelerating. It happens when you quickly take your foot off the pedal at any speed or revs.
    I suspected the throttle body because when i get somebody to press the pedal whilst i`m looking at the throttle body with the bonnett open it opens and closes but sort of rocks back and to a bit. I`m talking about the spring loaded bit that the throttle cable is linked to. is this the correct operation for it. Its hard to describe...
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 7, 2010]
    Does it feel like a large weight moving around? Almost like you've got a huge steel ball in the boot?

    Ours was doing that, and all the mounts were shot.
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  9. richie_jones
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    richie_jones Member

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    [Mar 7, 2010]
    No its definately an engine issue...Sometimes if you try and floor it after the jerking theres a total lack of power, if you lay off for a few seconds then accelerate its all ok again...
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  10. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Mar 7, 2010]
    Does this also happen when changing gear? From reading the above it could be a camchain fault, I had the cam chain tensioner & chain replace and everything was smooth again.
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  11. richie_jones
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    richie_jones Member

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    [Mar 7, 2010]
    Changing gear is fine. I have learnt to drive the car without the jerking happening. I do this by not laying off the accelerator to quickly and using the gears more to slow the car down. But when the missis gets in its a different story...
    The jerking is almost like a big misfire, so i was suspecting coil packs but like i said if i drive the car my way it won`t happen...
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  12. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Mar 7, 2010]
    I was able to do the same thing, but as you when my wife was driving the car it was terrible. That's why I booked it into the dealer and they replace the cam chain. Everything was OK once that was replace and I did not have to drive the car in a strange way.
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  13. richie_jones
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    richie_jones Member

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    [Mar 7, 2010]
    Could you explain why the camchain would cause this problem, i`m not to familiar with car mechanics...
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  14. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Mar 7, 2010]
    I cannot say, this was a good few years ago and the car had done around 160-180k miles. I booked the car in with Audi dealer with a fault that sounded like the above. So they had the car for a day, and they came up the cam chain fix, which I agreed to pay (cannot remember the price) I got the car back next day and it was running smoothly again. I guess if the chain or the tensioner is slack, then the engine would run lumpy when coming on and off the throttle!
    Last edited: Mar 7, 2010
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  15. Geeman
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    Geeman Low Life

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    [Mar 8, 2010]
    It does sound like a MAF problem to me. Mine was jerking/stalling/etc - turned out it was the connections though, not the MAF itself.

    I could run mine without the MAF even connected too!
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  16. richie_jones
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    richie_jones Member

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    [Mar 8, 2010]
    hi

    maf + n75 was the first 2 items i replaced. cars been doing it for 2 years, 30000 miles. geeman do you think it could be the cam chain.
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  17. Geeman
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    Geeman Low Life

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    [Mar 8, 2010]
    Cam Chain...? Apart from what B5Nut has just said about it, I've never heard of that being a problem.

    Could well be though...

    Mine turned out to be a wire that had been catching and had snapped for my N80 valve and dodgy connections to my MAF.
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  18. 951
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    951 Member

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    [Mar 9, 2010]
    Mine did exactly the same thing,sometimes it would hesitate on acceleration and sort of jerk slightly when comming off the throttle,i replaced the coil pack/plugs/leads/plug sensor/n75 valve/maf and a few other parts and in the end it turned out the turbo was on its was out !!
    #17
  19. mark_sarah
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    mark_sarah Limp mode!

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    [Mar 9, 2010]
    I had a few of these symtoms on my A3 1.8T sport.
    My car recently broke down on me. First symtoms was the jerky-ness, and pulling away slowly was a nightmare.
    When it finally broke completely, it would tick over fine, but the soon as you touched the accelerator it stalled.

    After reading a few links, i unplugged the MAF sensor, and found the car ran better than it had ever felt. So i replace the MAF sensor, and plugs, now the car runs like a dream.
    #18

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