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R1100S idles way too slow and tries to stall when hot - Why?
- Thread starter montliz
- Start date
roger 04 rt
New member
I was just looking rhough my BMW documentation for the various vintages of R1100S. As you said, it's Fuse 4.
I don't mean to bug you but any chance a friend can help you to measure the voltage between the grey and black wires of the O2 sensor? That would tell us if you're going lean and stalling or going rich and stalling.
roger 04 rt
New member
The hardest thing is piercing the wire without damaging it. Then attach the dvm to whatever you use to pierce the wire. Start the bike and watch the voltage as the idle drops off.
Success!
After much reading and learning and downloading, and, most importantly, a huge helping of advice, encouragement, tech tips, and PMs from roger 04 rt (Thanks, Roger!), we have fixed my beautiful S and it's running like a brand-new bike. Now it idles at a solid 1000-1050 rpms with no help from me and even warm-starts and idles without the assistance of the choke or throttle, just like it's supposed to. Whoa - it's never done that as long as I've had it.
With great feedback and input from the MOA oilhead group all the way, here's the sequence of events:
Returning home from a small trip, I find that the bike won't idle and tries to die anywhere below 1100 rpms. Not good; what to do?
I remove the Brass Bypass Screws and see that they're covered with gunk. That can't be good, so, figuring that the BBSs might not be the only thing needing a cleanup, I open up the airbox and remove the intake tubes and find that the inside of the airbox, the intake tubes, the throttle bodies, and the throttle plates are all covered with the sticky stuff. No wonder it won't run. So the throttle bodies come off and everything in sight gets returned to shiny as new, with new o-rings where needed.
---- Not related to my idle problem, but since I'm now looking right at it, I go ahead and replace the original cam chain tensioner with the new, improved version. Turns out to be the best hundred bucks I've spent on the bike, but back to the story ----
Back together again, I find that the bike runs great but still won't idle. It tries really hard, but no can do. Hmmmm.
Nick, the helpful and thoughtful service manager at Gulf Coast BMW in Houston, listens to the bike and says that it acts like the Motronic and TPS have so far not readjusted to my newly-cleaned intakes, and that the EFI may (may) adjust to the new dynamics in a few hundred miles if I don't want to just leave it there and get a ride home and let them scope it and fix it in their shop. Roger and Pauls1150 and Mark say hey that's great, but why wait? Just reset it yourself.
So, mechanical and cleanup possibilities exhausted, looks like it's time for little Johnny to go all 21st century and learn me some electronics.
New Radio Shack deluxe DVM in hand, and with much patient coaching and encouragement from Roger, I enter the brave new world of EFI.
Long story shortened (somewhat), we find that the O2 sensor reads more or less like it's supposed to but that the TPS shows hardly any voltage at what should be idle. AHA! So, with the help of a couple of hatpins and my precision rubber hammer, I read between pins 1 and 4 on the TPS and then precision-adjust it to 352 mv with key on, throttle closed, engine not running.
One fuse removal and Motronic reset later and the old girl is back! It's like a new bike.
Thing is, it's a beautiful machine with only 24K miles, but it's my first oilhead, and I had no idea how well it was supposed to run or what to look for or how to keep up with it. Thanks to you great folks, I'm way, way into it now. I'll probably never have to work on it again, but I'll keep in touch anyway, and thanks for everything!
Great to be here,
Johnny
After much reading and learning and downloading, and, most importantly, a huge helping of advice, encouragement, tech tips, and PMs from roger 04 rt (Thanks, Roger!), we have fixed my beautiful S and it's running like a brand-new bike. Now it idles at a solid 1000-1050 rpms with no help from me and even warm-starts and idles without the assistance of the choke or throttle, just like it's supposed to. Whoa - it's never done that as long as I've had it.
With great feedback and input from the MOA oilhead group all the way, here's the sequence of events:
Returning home from a small trip, I find that the bike won't idle and tries to die anywhere below 1100 rpms. Not good; what to do?
I remove the Brass Bypass Screws and see that they're covered with gunk. That can't be good, so, figuring that the BBSs might not be the only thing needing a cleanup, I open up the airbox and remove the intake tubes and find that the inside of the airbox, the intake tubes, the throttle bodies, and the throttle plates are all covered with the sticky stuff. No wonder it won't run. So the throttle bodies come off and everything in sight gets returned to shiny as new, with new o-rings where needed.
---- Not related to my idle problem, but since I'm now looking right at it, I go ahead and replace the original cam chain tensioner with the new, improved version. Turns out to be the best hundred bucks I've spent on the bike, but back to the story ----
Back together again, I find that the bike runs great but still won't idle. It tries really hard, but no can do. Hmmmm.
Nick, the helpful and thoughtful service manager at Gulf Coast BMW in Houston, listens to the bike and says that it acts like the Motronic and TPS have so far not readjusted to my newly-cleaned intakes, and that the EFI may (may) adjust to the new dynamics in a few hundred miles if I don't want to just leave it there and get a ride home and let them scope it and fix it in their shop. Roger and Pauls1150 and Mark say hey that's great, but why wait? Just reset it yourself.
So, mechanical and cleanup possibilities exhausted, looks like it's time for little Johnny to go all 21st century and learn me some electronics.
New Radio Shack deluxe DVM in hand, and with much patient coaching and encouragement from Roger, I enter the brave new world of EFI.
Long story shortened (somewhat), we find that the O2 sensor reads more or less like it's supposed to but that the TPS shows hardly any voltage at what should be idle. AHA! So, with the help of a couple of hatpins and my precision rubber hammer, I read between pins 1 and 4 on the TPS and then precision-adjust it to 352 mv with key on, throttle closed, engine not running.
One fuse removal and Motronic reset later and the old girl is back! It's like a new bike.
Thing is, it's a beautiful machine with only 24K miles, but it's my first oilhead, and I had no idea how well it was supposed to run or what to look for or how to keep up with it. Thanks to you great folks, I'm way, way into it now. I'll probably never have to work on it again, but I'll keep in touch anyway, and thanks for everything!
Great to be here,
Johnny
Last edited:
Great story, Johnny. Time to post a picture in the album at the top of this forum!
jwetering
New member
Great thread...especially the summary.
Mine's idling ok, but not great so I want to check my TPS voltage. Questions:
1: I assume I unplug the TPS and measure the voltage at pins 1 and 4 on the TPS itself rather than the cable. How does the TPS make voltage if it's not plugged in (and presumably without power) ?
2: If the voltage is out...where and what do I do to adjust this? You say you used a precision hammer.....but
Thanks
Mine's idling ok, but not great so I want to check my TPS voltage. Questions:
1: I assume I unplug the TPS and measure the voltage at pins 1 and 4 on the TPS itself rather than the cable. How does the TPS make voltage if it's not plugged in (and presumably without power) ?
2: If the voltage is out...where and what do I do to adjust this? You say you used a precision hammer.....but
Thanks
Hey Jasper,
I'm not the expert on this at all, but here's how you do it: Leave the TPS in place, slide the protective sheath down a half-inch or so until you have enough room to slip a couple of sewing needles (hatpins work great) up in there next to the pins. Hook your alligator clips from your voltmeter to the pins. Now turn the ignition on (don't start the bike) and read the voltage. If it's not right (optimum is 360 mv or a little less), you adjust it by slightly loosening the two screws that secure the TPS to the throttle body and then tapping the right or left side of it lightly with a rubber hammer in order to rotate it clockwise or counterclockwise until the voltmeter says what you want it to say. The TPS is connected to the outside end of the throttle shaft and it is adjusted by rotating it. Its easy to do but a few degrees of rotation make a lot of difference, so go slowly.
Hope that makes sense; sorry I'm not a better instructor.
Johnny
I'm not the expert on this at all, but here's how you do it: Leave the TPS in place, slide the protective sheath down a half-inch or so until you have enough room to slip a couple of sewing needles (hatpins work great) up in there next to the pins. Hook your alligator clips from your voltmeter to the pins. Now turn the ignition on (don't start the bike) and read the voltage. If it's not right (optimum is 360 mv or a little less), you adjust it by slightly loosening the two screws that secure the TPS to the throttle body and then tapping the right or left side of it lightly with a rubber hammer in order to rotate it clockwise or counterclockwise until the voltmeter says what you want it to say. The TPS is connected to the outside end of the throttle shaft and it is adjusted by rotating it. Its easy to do but a few degrees of rotation make a lot of difference, so go slowly.
Hope that makes sense; sorry I'm not a better instructor.
Johnny
m_stock10506
Well-known member
Johnny's description is very good. To be clear - yes, you have to keep the cable attached to the TPS. Once you have a voltmeter hooked up you are adjusting the position of the TPS by "tapping" it, just a tiny movement will change the voltage. Personally, I think .360 is too low - I would aim for the voltage to be about .370-.375.
jwetering
New member
These instruction could not be more clear. You should write shop manuals Johnny
Lord knows the BMW manual is somewhere between muted and muddled on the topic.I've adjusted the TPS on my K75 a few times already (and basically rewired a K1100LT) so I am very familiar with the principles .
Duly noted that 360 is not the max, but in the range. It will be interesting to see what mine reads. I've pulled my BBS already and they were moderately gunky. I sprayed some solvent in the holes while revving the engine, but this didn't make much of a difference. Will try again with better solvent I think.
My idle isn't horrible, I just feel it could be better.
cheers
jwetering
New member
Well....
I measure 800 mV to start - wow right ?
I turn the TPS until I read 370 mV. It's now cranked all the way over, but reading correctly so I leave it.
Pull the fuse and twiddle my thumbs for 10 minutes. Then replace the fuse, cycle the throttle three times.
Start the bike....no way, it's not able to hold an idle. wtf?
Check the voltage again and it's 71 mV !!??! wtf?
I adjust the TPS again to 370 mV, and it's more in the middle of the adjustment range.
Start the bike, runs nice, idles a bit high maybe.
Take it for a ride, it for sure wants to idle high (like 1300), so I turn in the two BBS a bit, and I think it's good but by now it's all hot and bothered, so we'll have to see how it behaves tomorrow.
I think it's better though...at least it's not idling low and lumpy any more.
I measure 800 mV to start - wow right ?
I turn the TPS until I read 370 mV. It's now cranked all the way over, but reading correctly so I leave it.
Pull the fuse and twiddle my thumbs for 10 minutes. Then replace the fuse, cycle the throttle three times.
Start the bike....no way, it's not able to hold an idle. wtf?
Check the voltage again and it's 71 mV !!??! wtf?
I adjust the TPS again to 370 mV, and it's more in the middle of the adjustment range.
Start the bike, runs nice, idles a bit high maybe.
Take it for a ride, it for sure wants to idle high (like 1300), so I turn in the two BBS a bit, and I think it's good but by now it's all hot and bothered, so we'll have to see how it behaves tomorrow.
I think it's better though...at least it's not idling low and lumpy any more.
roger 04 rt
New member
Michael, Although the correct voltage is widely stated as .370-.375, the source of that data seems to be the zero=zero procedure, which has a few big errors. True, you can get a bike to run using that procedure, but it doesn't end up set the way the Motronic expects, leading to poorer than ideal response at small throttle angles.
After examining the TPS and Motronic specifications, and extensive testing, 0.340 (340 mV) +/-15 mV is the correct target voltage for the TPS. http://forums.bmwmoa.org/showthread...yond-Zero-Zero&p=952354&viewfull=1#post952354.
roger 04 rt
New member
Well....
I measure 800 mV to start - wow right ?
I turn the TPS until I read 370 mV. It's now cranked all the way over, but reading correctly so I leave it.
Pull the fuse and twiddle my thumbs for 10 minutes. Then replace the fuse, cycle the throttle three times.
Start the bike....no way, it's not able to hold an idle. wtf?
Check the voltage again and it's 71 mV !!??! wtf?
I adjust the TPS again to 370 mV, and it's more in the middle of the adjustment range.
Start the bike, runs nice, idles a bit high maybe.
Take it for a ride, it for sure wants to idle high (like 1300), so I turn in the two BBS a bit, and I think it's good but by now it's all hot and bothered, so we'll have to see how it behaves tomorrow.
I think it's better though...at least it's not idling low and lumpy any more.
Jasper. It sounds as if your cables may not have been loosened properly before adjusting the TPS. Here is the BMW procedure for TB Sync: http://forums.bmwmoa.org/showthread...nd-Zero-Zero&p=1003851&viewfull=1#post1003851. When the cables are correctly loosened the TPS will remain stable unless your TB shafts are badly worn. If they are, with the cables loose, adjust the TPS with the engine idling, then the engine vacuum will fully close the butterfly.
jwetering
New member
Indeed, this might explain the strange measurements. I went back in this morning and adjusted the TPS to 345. Idled beautifully on my morning commute.
I will do a full setup this winter. It's good enough for the rest of this season.
