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Discussion Starter #1
Hello, guys! I'm a newbie on the forum, my name is Anton, I'm from Russia. I've got a problem with my 2000 K1200LT: it idles itself from 1500 rpm to 2000 rpm when warm. I started repairing my bike, because of high oil consumption: about 1l per 700 miles. Crankcase breather hose was broken and now is rempaced with a handmade one. I've cleaned the throttle body, repleced the valve seals, spark plugs, oxygen sensor (Denso DOX0117). Oil consumption is 250ml per 700 miles now. TPS and TVA were adjusted properly with the help of BMW ISTA+ Software (ex. Rheingold). New O-rings installed on the injectors. Sealing rings under the plastic intake stubs are checked and installed with a thin layer of sealant. Rubber intake stubs are checked and are also ok. Air and engine temperature sensors also seem to be fine. Fuel consumption is high: 24 MPG. I'll be gratefull for any advices, thanks in advance! Here is my video:
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Seems that it was some bug: I removed Motronic fuse for 15 minutes and now idle doesn't jump as on the video. When the engine is cold - everything is fine, but when warm - idle is 1500 rpm, not 950 as it should be. Oxygen sensor voltage is about 200mV. I've unpluged it and idle fell to 950 rpm. But when connecting oxygen sensor back - idle rises to 1500 rpm. Why does this happen?
 

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Seems that it was some bug: I removed Motronic fuse for 15 minutes and now idle doesn't jump as on the video. When the engine is cold - everything is fine, but when warm - idle is 1500 rpm, not 950 as it should be. Oxygen sensor voltage is about 200mV. I've unpluged it and idle fell to 950 rpm. But when connecting oxygen sensor back - idle rises to 1500 rpm. Why does this happen?

The oxygen sensor varies periodically during normal operation as the ecu varies air fuel mixture to fine tune. If unplugging it restores normal idle I would take that as a strong clue that it is bad. The best confirmation though would be to read it during operation with a GS-911 or an oscilloscope.
 
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The oxygen sensor varies periodically during normal operation as the ecu varies air fuel mixture to fine tune. If unplugging it restores normal idle I would take that as a strong clue that it is bad. The best confirmation though would be to read it during operation with a GS-911 or an oscilloscope.
Thanks! I don't have a GS-911, but I have ISTA+ (Rheingold) software on my notebook and K-L Line adapter, with the help of them I can receive live data from DME. What parameters should I look at? What can be the common reasons of idle normalization with unplugged O2 sensor?
 

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Thanks! I don't have a GS-911, but I have ISTA+ (Rheingold) software on my notebook and K-L Line adapter, with the help of them I can receive live data from DME. What parameters should I look at? What can be the common reasons of idle normalization with unplugged O2 sensor?
I don't know the details of BMW's control algorithm and thus don't know what the ECU would do with various oxygen sensor failure modes. I am not a lambda sensor expert, but most sensors can fail shorted or open at a minimum. I suspect the oxygen sensor could also get sluggish if coated with enough carbon and if the response was delayed compared to the fuel/air ratio adjustments, I am not sure what the computer would do. And I have no idea how the oxygen sensor fails should it be contaminated with leaded fuel for example.

Given the relatively modest price of the plug compatible Bosch sensor, I would buy one and try it.

Sailor has spent far more time studying the LT engine control system than have I so hopefully he will weigh in.
 

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You removed the ECU fuse but you do not mention resetting the TPS. Try it again and when you put the fuse back turn on the key but do not start. Rotate the throttle three time to full open and closed. Then turn off the key and follow with a normal start and see how that goes (keep the O2 plugged in).
 

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Discussion Starter #7
You removed the ECU fuse but you do not mention resetting the TPS. Try it again and when you put the fuse back turn on the key but do not start. Rotate the throttle three time to full open and closed. Then turn off the key and follow with a normal start and see how that goes (keep the O2 plugged in).
TPS reset has been performed - with no changes. The problem is detected: throttles are unsynchroned. 2 of 4 are a bit opened and a bit more air, than is required, goes to intake. O2 sensor sends the signal about much O2 in exhaust gas, ECU starts giving more fuel to compensate that and the idle increases. Seems that when my bike was consumpting much oil the idle decreased and the previous owner just screwed in 2 throttle adjusting screws for cylinders #1 and #2 to increase idle before selling it to me. Thanks for your advices!
 

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TPS reset has been performed - with no changes. The problem is detected: throttles are unsynchroned. 2 of 4 are a bit opened and a bit more air, than is required, goes to intake. O2 sensor sends the signal about much O2 in exhaust gas, ECU starts giving more fuel to compensate that and the idle increases. Seems that when my bike was consumpting much oil the idle decreased and the previous owner just screwed in 2 throttle adjusting screws for cylinders #1 and #2 to increase idle before selling it to me. Thanks for your advices!
How did you find the problem? Did you contact the previous owner?

Looks like you are well on your way to having a properly running LT..
 

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Discussion Starter #9 (Edited)
How did you find the problem? Did you contact the previous owner?

Looks like you are well on your way to having a properly running LT..
No, the previous owner said that he didn't do anything himself, the bike was repaired by his friends from BMW official workshop. When I bought my LT the final drive shaft was vibrating and knocking the swingarm from the inside. Seems that those guys from BMW official workshop just forgot to push it until it clicks and the cross aligns with the center of swingarm hole after changing the clutch. That's why I do everything myself. :) I replaced new Denso oxygen sensor with the old native one and tried to manually close each trottle by pushing them down near adjusting screws: on #3 and #4 the throttles didn't move, but on #1 and #2 they moved a bit and the idle decreased from 1500 to 950 rpm at once. I've screwed #1 screw for 1 and 1/8 turn and #2 screw for 1/4 turn, the idle is 1100 rpm now. So I'm going to borrow a carb synchronizing tool from my friend and adjust the throttle body properly.
 
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