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Erratic Revs on Start Up

Discussion in 'A3/S3 Forum (8L Chassis)' started by metricspaces, Aug 14, 2010.

  1. metricspaces
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    metricspaces Member

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    [Aug 14, 2010]
    Hi, I've an S3 8L and I'm seeing something strange - has anyone seen this before when starting up http://www.youtube.com/watch?v=5H1axtcj5MM ?

    When I start the engine from cold it jumps up to 1300 revs...then slowly works it's way up and down until it gets to about 900 revs. Almost as if it is doing a throttle body realignment.

    Last edited by a moderator: Aug 15, 2014
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  3. rlc1985
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    rlc1985 top gear

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  4. thegoal007
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    thegoal007 Another S3 owner....

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    [Aug 14, 2010]
    S3 8L - your rev counter has an analoge clock - mine don't have that ? it's an led one.
    #3
  5. murran
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    murran Active Member

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    [Aug 14, 2010]
    does it take slightly longer to start and seems very slightly down on power too?

    had one in at work few months ago and the crank sensor had gone down? was a similar complaint by the customer as what you describe. and weirdly enough, it didnt put the management light on despite the cranksensor fault being in the memory

    does it cut out if you unplug the cam sensor? it should make no difference plugged in or not on idle.
    when the cranksensor goes down, the engine management uses the cam signal to run the engine in a limp mode.
    #4
  6. thorsy22
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    thorsy22 Member

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    [Aug 14, 2010]
    Pretty sure mine jumps up to a similar level when cold but drops down to 720/760rpm according to vagcom and the dial when warm. I understand it to be the automatic choke, but if it stays at 900rpm that's a bit higher than mine. At a guess would say maf, coolant sensor, crank sensor anything to do with engine speed, air flow and temp that's off fooling the ecu into giving it more revs.
    I'm sure one of the more knowledgeable guys will be along shortly to correct me or give you the right answer.
    #5
  7. paneristi232
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    paneristi232 Member

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    [Aug 14, 2010]
    Its a non facelift S3 8L.

    J
    #6
  8. Madeley
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    Madeley Member VCDS Map User

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    [Aug 14, 2010]
    l have the same problem and my temp gauge takes along time to kick in, l put a new temp sensor in yesterday and l still l have the problem. This is odd.
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  9. Madeley
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    Madeley Member VCDS Map User

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    [Aug 14, 2010]
    Also check for vac leaks under the inlet manifold.
    #8
  10. drfeelgood
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    drfeelgood Member

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    [Aug 14, 2010]
    Thats exactly what mine does! I have changed the maf and coolant temp sensor, still there. I dont have any tempreture issues though, mine reads ok. must be the crank sensor?
    Last edited: Aug 14, 2010
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  11. metricspaces
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    metricspaces Member

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    [Aug 14, 2010]
    By the "fault being in the memory", do you mean it showed up when you did a diagnostic scan?

    I don't have anything shown up when I scan the engine module.

    Ive never tried unplugging the cam sensor...is there any online pictures or diagrams that might show me where it is, I could try it :)
    #10
  12. colicabcadam
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    colicabcadam Guest

    [Aug 14, 2010]
    mine does it, but it dies down pretty quickly, i thought i was simply a fast idle to help the car warm up / start up.
    #11
  13. drfeelgood
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    drfeelgood Member

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    [Aug 15, 2010]
    Yer i thought it was just something the car did when cold.
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  14. metricspaces
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    metricspaces Member

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    [Aug 15, 2010]
    I don't think so. My car never used to do this. Plus it doesn't happen consistently.

    If it was something "normal", then it would happen consistently on a cold start.

    For example, I've seen this on a cold start on days when it's 20+ degrees outside, and I haven't seen it on other days when it's a lot colder outside.
    #13
  15. drfeelgood
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    drfeelgood Member

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    [Aug 15, 2010]
    happens to mine consistently on a cold start, or any time over 7hrs, can anyone point to what the possible cause of this is?
    #14
  16. XFi
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    XFi Member

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    [Aug 15, 2010]
    Outside air temp does have an affect on this. But if the engine is cold it is cold regardless of the air temp. If the coolant was warm then this wouldn't really happen. Happens on my car every time I start it regardless of temperature.
    #15
  17. jdas03
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    jdas03 Member

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    [Aug 15, 2010]
    Same problem here, i presumed it was the maf... I am ordering a new one but sounds like it hasn't fixed your issues!
    Mine when cold turns over for ages and sort of chokes into life with revs around 1300 too after a minute or so dropping back to around 800! Seems quite common!
    #16
  18. [Dave B]
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    [Dave B] Daddy

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    [Aug 15, 2010]
    Mines recently started doing this, although i've seen no other side effects. Would be interested to know the reason.
    #17
  19. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Aug 15, 2010]
    Well mine does suffer from some of these issues, i know for a fact i have 3 vac leaks (2 are due to split rubber hoses in the pcv system and the other is my rocker cover gasket that is leaking) and i need a new maf, will be interesting to see if these 4 things when fixed will cure my problem.
    #18
  20. drfeelgood
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    drfeelgood Member

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    [Aug 15, 2010]
    I will take it into Audi and see what they say, However wont be for a while
    #19
  21. drfeelgood
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    drfeelgood Member

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    [Aug 15, 2010]
    You know i have a feeling a pipe is slightly spilt and causeing it to over rev untill it heats up and closes the slight spilt
    #20
  22. barters3
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    barters3 Member

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    [Aug 15, 2010]
    i have noticed mine has been doing this recently from cold. I have replaced the coolant temp sensor and the vac pipe arrangement under the inlet mani. I did not replace them to cure this particular fault though, i thought it was reasonable for the revs to do this from a cold start. I havent got vagcom so i think il keep an eye on it. Interesting to know the outcome of this thread tho....
    #21
  23. drfeelgood
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    drfeelgood Member

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    [Aug 15, 2010]
    I'am asking mechanics on that "just answer" , at 22 quid i better get a good answer lol
    #22
  24. s3dave
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    s3dave TFSI Hybrid Supporter

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    [Aug 15, 2010]
    oh dear.....
    #23
  25. metricspaces
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    metricspaces Member

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    [Aug 16, 2010]
    Yeah, think I will be looking at all the areas mentioned

    1) VAC leak - visual inspection & get it pressure tested
    2) Replace temp sensor- only a few pound, might as well
    3) Replace thermostat - only a few pound, might as well
    4) Replace crank sensor

    As for the MAF, I only replaced my MAF a year ago, doubt it's gone again, but might check that too. Anyone know how you'd check whether the MAF is causing this issue? The normal test for the MAF is running up to the redline and recording the airflow with VAGCOM...if this shows correct g/s figures, then you know the MAF isn't causing any performance issues, but could it still be causing this problem at low revs\start up?

    It would seem strange if it was the MAF. If you've a dodgy MAF, then you will always have performance problems. Whereas this startup issue is sporadic.
    #24
  26. Welly
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    Welly VX220 SC Driver :)

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    [Aug 16, 2010]
    Issues such as this are 99% down to vac leaks. Hunting at idle, erratic idle on cold start, they are all typical symptoms of vac leaks. So many have had them on here now...
    #25
  27. metricspaces
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    metricspaces Member

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    [Aug 16, 2010]
    Thanks. What's the best way to pin down where the leak is?
    #26
  28. Loupigs
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    Loupigs Member

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    [Aug 16, 2010]
    My 2002 A3 sort of did thism, fixed when the throttle body was cleaned out of all it's gunk.
    #27
  29. talentwalsh
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    talentwalsh Member

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    [Aug 18, 2010]
    I have the same issue, it gets worse when the engine is 30 deg +. Checked for leaks, cleaned the TB and no difference. Pretty sure its the crank sensor but at €110 im reluctant to change it. Does it take longer to fire than normal especially when warm? If so prob the crank sensor.
    #28
  30. Welly
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    Welly VX220 SC Driver :)

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    [Aug 18, 2010]
    Can't you get one from a scrapper to test before buying? That's what I'd be doing.....

    At least that way you can tell if your sensor is shot.
    #29
  31. Dane
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    Dane Faster than a V12 Q7

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    [Aug 18, 2010]
    Mine does this too and since changing the clutch switch did not solve my over revving problem when changing gear on boost, I reckon ive got some spilt pipes some where
    #30
  32. talentwalsh
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    talentwalsh Member

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    [Aug 19, 2010]
    Id love to check it Welly but S3's are as rare as three balled pitbulls in Ireland so no chance getting one from a scrapper. Im STILL waiting for my VCDS to arrive to see if it throws up a fault for it. Until then its crank and pray!!
    #31
  33. Welly
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    Welly VX220 SC Driver :)

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    [Aug 19, 2010]
    Bugger.....
    #32
  34. s3tle
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    s3tle Member

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    [Aug 20, 2010]
    Could this have anything to do with the PCV valve and the pipe which returns to the intake pipe?
    mine does something similar, hav just seen the the return pipe is degraded badly
    #33
  35. murran
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    murran Active Member

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    [Aug 20, 2010]
    the cam sensor is in a metal cap on the end of the inlet cam on the cambelt end of the engine. theres a 3 wire plug directly on to it.
    #34
  36. [Dave B]
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    [Dave B] Daddy

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    [Aug 26, 2010]
    Did anyone solve this? Have people with these symptoms recently changed any coilpacks?
    #35
  37. DaveA3
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    DaveA3 Audi A-Trizzle!

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    [Aug 26, 2010]
    did he clean his throttle body?
    #36
  38. hi456
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    hi456 New Member

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    [Aug 26, 2010]
    hi mine used to do that so i got fed up with it and tuck it to a higly recomended bosch master tech and it was just the coolant temp sender or loom to it he changed both as they were cheap, my car also turned over for abit before starting and cracked wen warm as if the timing was out but the sender and loom did cure this,
    however whilst on his computer he noticed it was running 15% lean but i didnt have the time or money to let him find out why any suggestions?
    thanks
    #37
  39. maxp
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    maxp Member

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    [Aug 26, 2010]
    For the car to rev higher when cold is totally normal.

    I had a look at mine on the drive home and it sat at about 1100 as i started it (so about 50rpm lower than yours), although I didnt hang about to see what happened after that.
    #38
  40. drfeelgood
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    drfeelgood Member

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    [Aug 27, 2010]
    I cleaned the throttle body, was a bit grubby, however problem is still there. its annoying as when cold, the increased revs give the car a slight jerky sensation when driving, also if going up a slight hill, the car continues to accerate even with the foot off the pedal. right werid it is. Its going to audi on wednesday, and im not takeing it back till its sorted! lol
    #39
  41. [Dave B]
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    [Dave B] Daddy

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    [Aug 28, 2010]
    This isn't totally normal, as mine didn't do it until the last few weeks (i've had it for 4 years). I've done a vagcom scan and it's coming up as running rich on bank 1, which just happens to be the same bank as the coilpack I replcaed recently. I'm going to replace the coilpack for a newer version (its currently an old one I had lying around) and see if that influences the idling issue (as the idle issue started around the same time as replacing the coil pack).
    #40

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