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Thread: Throttle Body Sync Questions

  1. #1
    Registered User jsouth's Avatar
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    Throttle Body Sync Questions

    My 2000 R1100RS has about 91,000 miles on it and has always surged a little and vibrated a little more than I think it should. I have owned it for the last 30,000 miles and do my own work. I am an experienced home mechanic and decided to tackle a "ground up" throttle body sync. (In hindsight, like a freaking idiot....)

    I have read all the IBMWR.org articles and have a TwinMax at my disposal. I got a wire into the red/white wire terminal and can read the voltage at the throttle position sensor. I got it set to 0.008V at no throttle opening (throttle stop screw backed off completely). I followed the advice to not rotate past the 0.008 (or lowest) reading. I tightened the TPS at this point. Then I used the throttle stop screw to obtain around 0.350V on the TPS and locked the throttle stop screw. So far, so good.

    I rotated the large brass air bleed screws all the way in and counted turns. Both were out more then 2.5 turns, but I set them at 1.5 turns out, as the instructions in one of the IBMWR articles suggested.

    Now I'm trying to get the RIGHT side throttle stop screw set and I can't get the bike to idle . It's trying to idle very low, and I would have to back out the bleed screws substantially in order to get it to idle, and I wonder if I will get an accurate setting of the right throttle stop screw in that case.

    QUESTIONS:
    • Should I go ahead and open the large brass air bleeds enough to idle and then go back and forth between adjustments to the right throttle stop and the air bleeds as I get closer to optimal settings?

    • Or should I open the left throttle stop screw for a reading of 0.370V or higher at the TPS (but less than 0.400V) in order to achieve a higher idle before making any more changes on the right?

    • Or have I screwed the pooch?

    • Any other tips on getting closer? I will have more time tonight and this weekend to devote to this project and I have a trip next week.


    I was a little surprised at how far I had to move the TPS to get to the 0.008V reading. I could see space at the stop screw, so I know I was reading a closed throttle plate.

    Thanks in advance for any help or moral support!

  2. #2
    Registered User roger 04 rt's Avatar
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    Zero=zero is an outdated procedure. The TPS isn't meant to be used below 250 mV per the parts spec. Have a read through this: https://forums.bmwmoa.org/showthread...yond-Zero-Zero.

    When you try to get the right throttle stop screw set, the engine needs to be hot. Try this outline:

    When you start zero=250 mV, the left throttle butterfly is fully closed. So the steps would be:

    --Clean TBs
    --Set TB BBSs to 2.5 turns (just a starting point) and make them equal.
    --Center and fully close both TB butterfly
    --Set TPS to 250 mV and lock TPS screws (no further adjustment of TPS)
    --Open left TB and count stop screw turns after contact until TPS reads 340 mV. Lock left stop screw (no further adjustment).
    --Set right TB stop screw open same number turns as left.
    --Start engine, warm up to at least 3 bars, balance idle using only right TB stop screw, do not touch BBS. Lock right TB stop screw.
    --Fully warm engine to 5 bars, the set idle & balance TB RPM to 1100 using BBS only
    --Remove cable slack per best procedure for R1100RT
    --Set TB balance at 2500 RPM using cable adjusters, per best procedure
    --Set Fast Idle speed to 2000-2200 rpm

  3. #3
    Registered User jsouth's Avatar
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    [QUOTE=roger 04 rt;1090297]Zero=zero is an outdated procedure. The TPS isn't meant to be used below 250 mV per the parts spec. Have a read through this: https://forums.bmwmoa.org/showthread...yond-Zero-Zero.

    Will do. I have actually seen and read that once, but couldn't find it when I started this debacle. It will obviously be much more meaningful when I have had my hands on the parts in question already! Thanks for your help. I'll try your suggestions tonight.

    I wonder why IBMWR hasn't updated that info? It's still in the R1100 maintenance PDF and on the ibmwr.org site.

  4. #4
    MOA #24991 Pauls1150's Avatar
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    While the procedure is not updated, it does actually work - it just means that the mapping is offset by that ~250 mV, and the computer WILL compensate for this after a few rides. But Bosch doesn't spec it that way, and nobody (here at least) knew about it until Roger actually dug into this!

    But getting back to the original point - What isn't mentioned regarding the Big Brass Screws: They should be pulled Completely Out and closely inspected for crapitation buildup - it will be there, and there will also be more buildup inside the tiny little Idle Air Passageway, at the bottom, where the screws actually do their air setting.

    The screws can be wiped off with gas or alcohol and a rag; if the O-rings are cracked, it would be worthwhile to buy a new pair of screws. NOTE there are TWO sizes of screws, "early" and "late" - take one of your old ones with you just to be sure you get the right ones (early ones are slimmer). They're about $6/each, and BMW won't sell you just the silly O-ring.

    To clean the passageway, you can use a high-pressure can of carb cleaner (GOGGLES!!!) and a couple of Q-tips.

  5. #5
    Registered User dieselyoda's Avatar
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    The zero-zero method isn't outdated, just rogers method is a hair more precise and that's about it. As Pauls said, the Motronic is pretty forgiving with the actual TPS voltage.

    However "crapitation" is very often overlooked and I do the de-crapitation on every oilhead I get for a sync and a lot my inconsistent results disappeared.

    Most important about throttle sync, new/good plugs, valve adjustment, clean air filter and making damn sure you aren't fighting worn TB shaft bushings.
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case, my baby, fast, fun)
    3xR90/6, two just sold, one for a sidecar. 1983 K100RS (Cafe now)
    Very Rough R80RT. 1987 K1100RS (freaking hooped I think)

  6. #6
    Registered User jsouth's Avatar
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    Quote Originally Posted by Pauls1150 View Post
    While the procedure is not updated, it does actually work - it just means that the mapping is offset by that ~250 mV, and the computer WILL compensate for this after a few rides. But Bosch doesn't spec it that way, and nobody (here at least) knew about it until Roger actually dug into this!

    But getting back to the original point - What isn't mentioned regarding the Big Brass Screws: They should be pulled Completely Out and closely inspected for crapitation buildup - it will be there, and there will also be more buildup inside the tiny little Idle Air Passageway, at the bottom, where the screws actually do their air setting.
    Thank you -- I will clean those as well.

  7. #7
    Registered User jsouth's Avatar
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    Quote Originally Posted by dieselyoda View Post
    Most important about throttle sync, new/good plugs, valve adjustment, clean air filter and making damn sure you aren't fighting worn TB shaft bushings.
    I just did the valve adjustment very carefully using the four feeler gauge method, plugs are good and within replacement mileage interval, and so is air filter. Worn TB shaft bushings are a definite possibility, but I haven't noticed a problem. I'll spray some WD-40 around the shaft ends when I get a decent idle and see if anything changes. Thank you for the suggestions.

  8. #8
    Registered User jsouth's Avatar
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    Latest attempt:

    - Cleaned Throttle bodies (not terrible but dirty)
    - Cleaned Air Bleed Screws and passages (BBS) (lots of gunk)
    - Set 0 TB opening = 0.250V
    - Adjusted left stop screw for 0.340V, counting turns (took only 3/8 turn)
    - Adjusted right stop screw for 3/8 turn open

    Bike immediately idled better than previous attempt, but still very rough.

    I do hear the TB shafts rattling (more on right side but present on both sides) so re-bushing is needed, but I'm leaving for a trip Wednesday and can't get that done before then. It was running decently before I started so I know there is a setting somewhere that will work.

    I pulled the air screws one at a time while it was running and there is strong vacuum on both so I know they are definitely clear. The throttle cables are loose on both sides (it's a 2000 model).

    As I try to balance at idle, I can get the right stop screw completely off the stop (throttle closed 100%) and it still is biased to that side. I think the right TB shaft is worn severely enough that the leakage on that side is greater than the opening on the left side TB.

    Should I go ahead and open the left side a little more, and get the sensor voltage no more than 0.370V or 0.380V? Then try to balance again? It seems I cannot close the right side enough to match, probably because of the worn shaft.

    Any other suggestions for a decent compromise setting?

  9. #9
    Registered User roger 04 rt's Avatar
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    Yes, go to 380 mV that will be another 0.16 degrees. If you do that and it works, back the TPS down to 340 mV by loosening the TPS and adjusting it before adjusting idle speed with the BBS.

  10. #10
    Registered User jsouth's Avatar
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    Quote Originally Posted by roger 04 rt View Post
    Yes, go to 380 mV that will be another 0.16 degrees. If you do that and it works, back the TPS down to 340 mV by loosening the TPS and adjusting it before adjusting idle speed with the BBS.
    I had considered doing exactly that but was afraid it would make it run too lean at cruise. I'll try it now! Thanks, Roger. BTW, the battery has been great with multiple restarts.

  11. #11
    Registered User roger 04 rt's Avatar
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    It won't cause any additional leanness. This is just a method to get TB alignment left to right and to the Motronic. AFR is unaffected.

  12. #12
    Registered User dieselyoda's Avatar
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    You can't get balance from the TPS no matter what you do. All the TPS does is send a signal to the Motronic to give an indication as to throttle plate angle. If you start with the wrong throttle plate angle and adjust the TPS voltage within specs, you still have the wrong throttle plate angle.

    Of course, I mentioned loose/leaking TB shafts and if you have one that is loose, you will chase balance just like my dog chases deer thinking he just wants to play with them.

    Bottom line, you are trying to get the right amount of air into each cylinder so when they fire, they are even. You have an idle balance that I usually don't pay much attention to but the real balance comes at your cruise RPM. A smooth idle is fine but a vibration at speed will give you a pile of symptoms that you feel in your body starting with numb hands and a numb butt.
    1997 R1100RT (Restored Basket Case) , 1981 KZ 440 LTD (Restored Basket Case, my baby, fast, fun)
    3xR90/6, two just sold, one for a sidecar. 1983 K100RS (Cafe now)
    Very Rough R80RT. 1987 K1100RS (freaking hooped I think)

  13. #13
    Registered User jsouth's Avatar
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    Quote Originally Posted by dieselyoda View Post
    You can't get balance from the TPS no matter what you do. All the TPS does is send a signal to the Motronic to give an indication as to throttle plate angle. If you start with the wrong throttle plate angle and adjust the TPS voltage within specs, you still have the wrong throttle plate angle.

    Of course, I mentioned loose/leaking TB shafts and if you have one that is loose, you will chase balance just like my dog chases deer thinking he just wants to play with them.

    Bottom line, you are trying to get the right amount of air into each cylinder so when they fire, they are even. You have an idle balance that I usually don't pay much attention to but the real balance comes at your cruise RPM. A smooth idle is fine but a vibration at speed will give you a pile of symptoms that you feel in your body starting with numb hands and a numb butt.
    You nailed it when you mentioned loose TB shafts. Right side is rattling, and impossible to adjust repeatably. I'll rebuild as soon as I get back from my trip and send in my HES for rewiring at the same time. My trip has been planned for some time and juggling the schedule between the three of us is impossible. I'll keep chasing until I get back to decent and settle for that.

    Starting in 2007, my dad (now 77), brother, and I take a long trip every year. My folks married young so there are only 18 years between my dad and I. The trip is a cool tradition and I'm not going to be the cause of it not happening this year come hell or high water. This year, we aren't carving as many twisties as in years past, but we will be seeing some cool and historic sites along the Texas gulf coast (and enjoying the company of family).

    Thanks to everyone for the advice and help!

  14. #14
    Registered User jsouth's Avatar
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    UPDATE --

    All my problems were caused by user error on the Twinmax. I assumed (and yes the adage about assuming is true) that the meter swung towards the strongest vacuum. The instructions say nothing about this, just to adjust based on what the reading is.

    Once I figured out that the needle was swinging to the WEAKEST vacuum, things got better really fast. I went back to the very beginning, set closed throttle = 0.250V, then opened until a reading of 0.340V. Set the other side the same opening. Then, reading the Twinmax correctly, I was able to get balanced at idle and at 3500-4000 RPMS, even at MAX sensitivity.

    I still will need to rebuild the shafts, but they are not causing an issue other than slight noise. Idle is good and off-idle is a smooth transition, and cruising RPM is balanced. A quick 70-mile ride confirmed the smoothness and power. Ready for the trip.

    Again, thanks to everyone here for the great advice.
    Last edited by jsouth; 05-21-2017 at 11:51 PM.

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