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Thread: Passat B5 starts and idles but no throttle until warm

  1. #1
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    Passat B5 starts and idles but no throttle until warm

    I first posted about this issue several months ago and despite many suggestions from this forum I am still trying to solve this mysterious problem. Rain and frustration has hindered my efforts the past few months but Iím ready to dig in again and would appreciate any input.

    My car is a 2005 B5.5 Passat TDI Wagon with a BHW engine. It has 140,000 miles on it and the engine ran perfectly last fall when I began a manual transmission swap. I opted to pull the engine and AT out of the car as a unit and while the engine was out of the car I had a shop do a BSM delete and new timing belt and water pump. I also installed a new coolant manifold, water temp sensor, and engine speed sensor. The transmission is an FHN from Dutch Auto Parts and the rest of the manual swap parts were from a 2002 Passat V6. Iím currently using an ECU with an immobilizer delete that works just fine in my friendís Passat.

    I completed the swap last October and the engine has not run normally since then. This is the current situation when I try to start it:
    The cold car starts immediately but starts at a low rough idle, around 450 rpm, which increases to around 950 rpm over a couple of seconds at which point the engine usually shuts down. After a few tries like this instead of shutting down completely it will catch itself and idle very roughly at 450-500 rpm. At this point there is no throttle response (VCDS shows the TPS operating properly), the timing is at 13-14 BTDC, the Specified MAF (SMAF) is 650-850 while the Actual MAF (AMAF) is around 450, and the IQ is 33.8.

    It will idle in this condition and gradually warm up. As the coolant temp rises the rpm slowly increases and gets smoother. The throttle remains unresponsive and the timing and SMAF are unchanged. When the coolant temp reaches 56-58 C everything changes-
    the idle is smooth and stable at 850 rpm, the throttle is responsive, the timing is within normal specs (1.6 BTDC), the SMAF and AMAF are approximately the same in the 250-450 range, and the IQ is 4.7 The engine revs normally to redline and if I shut it down and restart it, the car runs normally.

    The only codes on a VCDS Autoscan are related to the missing TCM which should not effect whether the engine runs properly or not. I have tried 3 coolant temp sensors, the last one from the VW dealer with no change. Iím confident that this is not an ECU issue and Iíve tried a different MAF sensor from my friendís Passat without any change.

    Anybody seen anything like this before? Calling all TDI geniuses to help me get this car on the road. Many thanks.

  2. #2
    NostraJackAss Jack@European_Parts's Avatar
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    Sounds like warn injectors & or cam followers to me ......have you observed them?

    Post an auto-scan
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    Thanks for your thoughts. The engine ran perfectly before the manual swap. Seems unlikely that something happened to the injectors or cam followers while the engine was out of the car. I'll post an autoscan later but as I said in my post NO codes other than missing TCM.

  5. #4
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    the auto-scan is request not necessarily just for the fault codes, but to see what all components are installed/recognized.

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    FoRT jyoung8607's Avatar
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    Quote Originally Posted by tdidaho View Post
    The only codes on a VCDS Autoscan are related to the missing TCM which should not effect whether the engine runs properly or not.
    You have an auto ECU with cold startup fuel enrichment maps designed to meet a certain baseline torque load. Even in Park or Neutral, that load included a spinning torque converter and a working ATF pump. You disappeared those things, PLUS you disappeared your balance shaft load. Just spit-balling here, but everything you've shared above could be consistent with the ECU running out of room to compensate, trying to clamp down on unexpectedly high RPM from the commanded IQ and timing.

    Maps for auto vs. manual ECUs are subtly different, including startup behavior. That's why there are different ECUs (yes really just software) instead of just a coding bit. Why not reflash or replace your ECU with the manual variant, like you need to do anyway to get rid of your MIL, and see what that does for you.

    Jason

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    this isn't the first guy with the swap so i don't think coding or software is the issue. did u pull on a wire or connector pulling the trans out or in. have u checked torsion values cold and hot.

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    Benevolent Dictator Uwe's Avatar
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    Quote Originally Posted by jyoung8607 View Post
    Why not reflash or replace your ECU with the manual variant, like you need to do anyway to get rid of your MIL, and see what that does for you.
    My recollection is that the TDI engine installed in the NAR 2005 Passat was mechanically unique, and it was never offered in combination with a manual trans. If I'm correct, that leaves things pretty much in the same spot as the 2001-2003 24V VR6 Eurovans, where there simply is no MT ECU or ECU software for that engine.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

  10. #8
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    Quote Originally Posted by D-Dub View Post
    the auto-scan is request not necessarily just for the fault codes, but to see what all components are installed/recognized.
    I'll get an autoscan later today

  11. #9
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    Quote Originally Posted by jyoung8607 View Post
    You have an auto ECU with cold startup fuel enrichment maps designed to meet a certain baseline torque load. Even in Park or Neutral, that load included a spinning torque converter and a working ATF pump. You disappeared those things, PLUS you disappeared your balance shaft load. Just spit-balling here, but everything you've shared above could be consistent with the ECU running out of room to compensate, trying to clamp down on unexpectedly high RPM from the commanded IQ and timing.

    Maps for auto vs. manual ECUs are subtly different, including startup behavior. That's why there are different ECUs (yes really just software) instead of just a coding bit. Why not reflash or replace your ECU with the manual variant, like you need to do anyway to get rid of your MIL, and see what that does for you.

    Jason
    I have an ECU that is flashed for a manual transmission. It works once the car is warmed up but for some reason doesn't allow the car to idle poorly long enough to warm up. Plenty of people have done this swap and been able to start and run the engine with the stock AT tuning. It doesn't run well but it runs.

  12. #10
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    Quote Originally Posted by ivagp View Post
    this isn't the first guy with the swap so i don't think coding or software is the issue. did u pull on a wire or connector pulling the trans out or in. have u checked torsion values cold and hot.
    where do I check torsion value?

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