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    Thread: Rev hang... what actually causes it?

    1. 04-06-2011 12:34 AM #1
      So I have done a search on this topic and only found the solution of a bad clutch sensor. (For those that don't know what rev hang is, it in the hanging/increase in rpm when the clutch is pushed in to shift gears).
      My cars cruise didn't work when I got it so I installed a new one and cruise worked afterwards (which if the sensor was no good, it wouldn't).
      I'm sure I'm not the only one with this happening to them, so what are other people doing to solve it?

      Thanks in advance!

    2. Moderator groggory's Avatar
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      04-06-2011 02:46 AM #2
      Just an idea...but try a throttle body alignment.
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    3. Member schwartzmagic's Avatar
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      04-06-2011 10:45 AM #3
      The Uni 830 file I have gives me rev hang. Not too bad, but it is annoying. Its gotten worse lately but that might be because of my exhaust leak

    4. Moderator groggory's Avatar
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      04-06-2011 11:06 AM #4
      Quote Originally Posted by schwartzmagic View Post
      The Uni 830 file I have gives me rev hang. Not too bad, but it is annoying. Its gotten worse lately but that might be because of my exhaust leak
      I hear people blame rev hang on exhaust leaks too. And I noticed that as my exhaust leak got worse, the rev hang got worse. I'm fixing my exhaust leak SOON and so I'll report back if the rev hang goes away. Maybe the engine is getting bad data from the O2 sensors, and as such doesn't run all that great.
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      04-06-2011 11:19 AM #5
      Depends where the exhaust leak is. If it's after the first o2 sensor, it doesn't really matter as much. I've been told the rear o2 is there for nothing other than the OBD2 scan to tell e-check if your cat is working/there.

      Front o2 does the engine management stuff as far as air/fuel.

    6. Member elRey's Avatar
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      04-06-2011 11:37 AM #6
      vagcom block #66. check second(or third) value while pressing/depressing clutch pedal. one of the bits should toggle 0/1

    7. Member herb2k's Avatar
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      04-06-2011 02:58 PM #7
      Quote Originally Posted by elRey View Post
      vagcom block #66. check second(or third) value while pressing/depressing clutch pedal. one of the bits should toggle 0/1
      I had that problem. Replaced clutch switch F36 ($50 part from dealer) and all was good!

    8. 04-06-2011 03:02 PM #8
      My car is all stock and there is definately no exhaust leak. I will have to see what the stealership wants for a TB allignment as I don't have Vagcom (or Ross Tech or whatever its called now).

      I guess my next question, is there somewhere to pick up the Vagcom/Ross tech program for a cheaper price? I see its 249 on Ross techs site.
      Or is there a different program I can get that will allow me to diagnose and adjust the computer?

    9. Member 01TornadoWolf's Avatar
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      04-06-2011 05:26 PM #9
      Quote Originally Posted by elRey View Post
      vagcom block #66. check second(or third) value while pressing/depressing clutch pedal. one of the bits should toggle 0/1
      look at block 66: http://www.ross-tech.com/vag-com/m_blocks/060-069.html

      if u dont have vagcom, check around. i guarantee someone local has one.

      i had nasty rev hang but my cc still worked. block 66 showed clutch signal at ecu wasnt changing. clutch switch was fine, actually turned out to be my ecu!
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    10. Member Three3Se7en's Avatar
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      04-06-2011 06:00 PM #10
      My eurodyne 630 flash has nasty rev hang.
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    11. 04-12-2011 11:01 AM #11
      So I got lookin a little further... I have 3 PCV hoses that are completely $%@#ed. Ordering some new ones from 034Motorsport this morning. Hopefully this is my problem.

    12. 04-17-2011 10:12 PM #12
      Got all my hoses changed but still no luck gettin rid of the rev hang. I'll be getting chipped by APR in 3 days so I will have to try that throttle body alignment after that and post my findings

    13. 04-26-2011 12:00 PM #13
      Tried the throttle body adaption and still no luck. The hang is definately less noticable with the apr program running, but it is still there.

      Any other ideas?

    14. Member schwartzmagic's Avatar
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      04-26-2011 02:00 PM #14
      Have you tried checking for exhaust leaks or pressure testing your charge pipes? Just a thought......

      I had all kinds of issues because of a boost leak right off the coupler on the compressor housing. My axle was rubbing on the tbolt clamp that tightens the coupler on the compressor exit and eventually got eaten away by the axle, no more clamping = boost leak. The boost leak was throwing off my idle and AFRs.

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    15. Moderator groggory's Avatar
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      04-26-2011 02:43 PM #15
      Quote Originally Posted by schwartzmagic View Post
      Have you tried checking for exhaust leaks or pressure testing your charge pipes? Just a thought......

      I had all kinds of issues because of a boost leak right off the coupler on the compressor housing. My axle was rubbing on the tbolt clamp that tightens the coupler on the compressor exit and eventually got eaten away by the axle, no more clamping = boost leak. The boost leak was throwing off my idle and AFRs.

      Sent from my MB860 using Tapatalk
      I second this. I hear people saying on here all the time that they 'checked' and have no leaks. But to know you gotta test. Not just eyeball it or feel around.

      Turbo cars do not like air leaks. They live on the air. They get angry when you take or give air at the wrong times.
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      07-21-2014 11:13 AM #16
      How much would each of those things cost?

      The throttle body alignment and the pressure test on the charge pipes?

    17. Member burkechrs1's Avatar
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      07-21-2014 11:46 AM #17
      Quote Originally Posted by RafaGti View Post
      How much would each of those things cost?

      The throttle body alignment and the pressure test on the charge pipes?
      If you know of a VW specific shop (not dealership) you may be able to go there and they can do a throttle body alignment with a VAG-COM. Takes about 60 seconds. The pressure test, shouldn't cost you more than $40 to make one, as long as you have access to compressed air.

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      07-21-2014 01:16 PM #18
      Quote Originally Posted by burkechrs1 View Post
      If you know of a VW specific shop (not dealership) you may be able to go there and they can do a throttle body alignment with a VAG-COM. Takes about 60 seconds. The pressure test, shouldn't cost you more than $40 to make one, as long as you have access to compressed air.
      Thanks for the help. Ill start looking for a place to get this done. Ive already replaced the switch and its still holding/reving between gear changes.

    19. Member David_Tedder's Avatar
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      07-21-2014 03:09 PM #19
      I also experience this and would love to see what the outcome is
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    20. Member gitman's Avatar
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      07-21-2014 03:27 PM #20
      Quote Originally Posted by David_Tedder View Post
      I also experience this and would love to see what the outcome is
      have you also replaced your clutch position switch? i think the tell-tale symptom for this is if you disengage cruise control by pressing in the clutch, and witnessing the RPMs not only hang, but climb up before finally going down.

      edit: i used this DIY: http://forums.vwvortex.com/showthrea...l)-replacement
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      07-21-2014 03:47 PM #21
      Quote Originally Posted by gitman View Post
      have you also replaced your clutch position switch? i think the tell-tale symptom for this is if you disengage cruise control by pressing in the clutch, and witnessing the RPMs not only hang, but climb up before finally going down.

      edit: i used this DIY: http://forums.vwvortex.com/showthrea...l)-replacement
      Yes sir. I tried the pressing the clutch in and the revs did climb before eventually going down.

      Its so annoying, specially in the upper RPM range if youre tryiing to shift even remotely fast or hard.

    22. Member gitman's Avatar
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      07-21-2014 03:56 PM #22
      Quote Originally Posted by RafaGti View Post
      Yes sir. I tried the pressing the clutch in and the revs did climb before eventually going down.

      Its so annoying, specially in the upper RPM range if youre tryiing to shift even remotely fast or hard.
      sorry, my question was directed at David_Tedder who did not specify whether he had done the clutch switch.
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    23. Member David_Tedder's Avatar
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      07-21-2014 06:27 PM #23
      I haven't done the switch because up until today and seeing this thread I hadn't put much thought into what was causing it as there is too many things changed with my build
      Last edited by David_Tedder; 07-21-2014 at 06:27 PM. Reason: error
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    24. 07-22-2014 03:03 AM #24
      I had rev hang when I used a 70mm TB with an Eurodyne file for 60mm TB, with a maffless setup.
      Once the correct 70mmTB file was flashed, the rev hang dissapeared, in spite of the bug with the clutch switch (a bug in the software disables the switch, this only affects the CC).

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      07-22-2014 04:35 AM #25
      Quote Originally Posted by rogerius View Post
      I had rev hang when I used a 70mm TB with an Eurodyne file for 60mm TB, with a maffless setup.
      Once the correct 70mmTB file was flashed, the rev hang dissapeared, in spite of the bug with the clutch switch (a bug in the software disables the switch, this only affects the CC).
      Wait wait.... Eurodyne software... has a bug?

    26. 07-22-2014 12:03 PM #26
      check ur clutch switch in MB066 of VCDS. Report here if u see the bits changing 0 to 1 when u press the pedal. I am curious...

    27. Member RodgertheRabit II's Avatar
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      07-23-2014 09:47 AM #27
      Quote Originally Posted by rogerius View Post
      I had rev hang when I used a 70mm TB with an Eurodyne file for 60mm TB, with a maffless setup.
      Once the correct 70mmTB file was flashed, the rev hang dissapeared, in spite of the bug with the clutch switch (a bug in the software disables the switch, this only affects the CC).
      Mine does the same thing. Does it a little on the Stock TB and a base 630 file. What did you adjust to fix it?

    28. Member l88m22vette's Avatar
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      07-23-2014 01:03 PM #28
      As a general answer, rev hang occurs to let as much fuel as possible burn past once the acceleration/cruising interval is over...you let off the gas, and for a second (or whatever) there is still fuel going into the engine for either acceleration or typical driving, but that fuel might not get burnt because the engine is no longer operating in a partial/full throttle mode. Unburnt fuel causes both increased emissions and damage to the catalytic converter, both big no-nos for OEMs (this also causes the cool-ass flame spitting you see on race cars, which occurs while braking/decelerating).
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    29. Member gitman's Avatar
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      07-23-2014 01:38 PM #29
      Quote Originally Posted by l88m22vette View Post
      As a general answer, rev hang occurs to let as much fuel as possible burn past once the acceleration/cruising interval is over...you let off the gas, and for a second (or whatever) there is still fuel going into the engine for either acceleration or typical driving, but that fuel might not get burnt because the engine is no longer operating in a partial/full throttle mode. Unburnt fuel causes both increased emissions and damage to the catalytic converter, both big no-nos for OEMs (this also causes the cool-ass flame spitting you see on race cars, which occurs while braking/decelerating).
      i can only speak for myself but i hope that for the purposes of this discussion everyone is referring to rev hang with an abnormally long duration, and even rev climb. what you're referencing should be considered normal behavior.
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    30. Member RodgertheRabit II's Avatar
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      07-23-2014 01:49 PM #30
      Yes, this is beyond the "normal behavior"

    31. Member Brake Weight's Avatar
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      07-23-2014 03:09 PM #31
      Do these cars suffering from this have a cable TB? Or are they 'fly by wire?' My GLI is the latter, and compared to my cable operated Tacoma it's a bit different. I have to adjust to the two differences between them. As in, in my VW I lift off the gas prior to shifting. In my Taco, I do it simultaneously.

      Just something to consider.
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      07-23-2014 06:31 PM #32
      Mine is dbw and at full throttle if you were to do it at the same time the rpm will flare up 500rpm almost , I too have to let off gas just before clutching in
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      07-23-2014 09:55 PM #33
      After swapping from my truck to my VW, it'll take a run through the gears to get used to it again.
      Quote Originally Posted by Anony00GT View Post
      Who's the idiot that deleted the EVAP solenoid?
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      ...There two types of Americans: those who lived through the Carter years and those who are about to.

    34. 07-24-2014 02:33 AM #34
      Quote Originally Posted by RodgertheRabit II View Post
      Mine does the same thing. Does it a little on the Stock TB and a base 630 file. What did you adjust to fix it?
      I asked the Eurodyne dealer to flash the correct Alpha-N from a 70mm TB base file. Problem solved, no more annoing rev hang (long duration/high rpm climb).
      I only have now the normal rich condition at throttle lift off, for 1-2 seconds, as I see on the wide band AFM.

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      07-24-2014 07:02 AM #35
      Quote Originally Posted by ScubaStevo87 View Post
      My car is all stock and there is definately no exhaust leak. I will have to see what the stealership wants for a TB allignment as I don't have Vagcom (or Ross Tech or whatever its called now).

      I guess my next question, is there somewhere to pick up the Vagcom/Ross tech program for a cheaper price? I see its 249 on Ross techs site.
      Or is there a different program I can get that will allow me to diagnose and adjust the computer?
      E-Bay cable for $25 to $30 and VCDS Lite for $99 from Ross-Tech. That's all you need.

      Throttle Body Alignment is critical to the proper operation of the throttle. Rev hang is just one symptom of a bad TBA, but it is one of the most common. A TBA is necessary after any battery disconnect or removal of electrical terminal at throttle body. Doesn't hurt after a cleaning either.

      If you go to the Vortex VAG-COM Forum, there is a locator thread there that shows who is nearby that has a VAG-COM and may be able to assist you. Very handy service. Bring

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