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Engine stalling when slowing - test idle control device?

It is waiting for replacement but I am pretty sure it is not the problem. The code from O2 says the mixture is too leśna, but the sensor itself is working ok.

I will replace it the during the next weekend and report back results

@Edit

No difference after change. So it is not O2 sensor.
 
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I have finally managed to install ISTA+ with K-DCAN cable. I have done full reset of all sensors and adapted idle motor and TPS. Since then I have made about 700km in hot conditions and it has not stalled a single time! Not even single RPM drop. Fingers crossed, but it looks like it has needed a proper soft reset, not just a battery unplugging.
 
Let me add to this thread and confirm that, indeed, cracked idle air contol valve hoses do cause stalling at idle.
Yesterday, for the first time in about maybe a month, I rode my C650 Sport to the gym, a 16 mile ride each way.
To my surprise, at the first stop sign I encountered, after about 10 miles, the engine cut out. I restarted it without issue, and it did not happen again for the remaining 6 miles. However, when I went to ride back home after my workout, it stalled at the very next traffic light, less than a mile. It then stalled at the next light after that, and the next one after that, and so on. Sometime it would 'struggle' to keep running, but would inevitably stall. Each time it would restart without any problem, however I would have about a second to launch the bike, or it would again stall. The last 10 miles were without any traffic lights or stop signs, and to my somewhat surprise, it did not stall when I got home and parked the bike. Still, obviously an issue.
Scanned the codes and I got 'Lambda sensor 01' fault code no 3A2020 on the Motoscan. I went ahead and ordered a NOS O2 sensor (part no 11787716654) after taking out and verifying the original one. But then I reread this thread and decided to also inspect the vacuum/air lines going to the idle air control valve. I had done so once before, in around 2023, and found one beginning to crack. I replaced that one, but the other one looked in ok shape. Well, today that other one is VERY cracked!

20260115_123505.webp

Luckily, in 2023 I had bought 2 new ones, so I was able to install the new one right away.

20260115_123548.webp

I will still also install the new O2 sensor (can't hurt and the NOS one was only $70 as opposed to BMW's current friendly price of $450) and also install one of my 4 new mechanical timing chain tensioners. The current one (3rd one since new, the bike has 20K miles now) started to every once in a while make a faint death rattle so I figure now's the time. I bought 4 when that batch came up on Ebay for (as I recall something like) $110, so "cheap insurance" on that other common and massive problem plaguing these otherwise wonderful machines.

Will report back when I have it all back together but I am 99% confident the new idle air hose will fix the stalling issue.
 
Ceesie76 said:
Let me add to this thread and confirm that, indeed, cracked idle air contol valve hoses do cause stalling at idle.
Yesterday, for the first time in about maybe a month, I rode my C650 Sport to the gym, a 16 mile ride each way.
To my surprise, at the first stop sign I encountered, after about 10 miles, the engine cut out. I restarted it without issue, and it did not happen again for the remaining 6 miles. However, when I went to ride back home after my workout, it stalled at the very next traffic light, less than a mile. It then stalled at the next light after that, and the next one after that, and so on. Sometime it would 'struggle' to keep running, but would inevitably stall. Each time it would restart without any problem, however I would have about a second to launch the bike, or it would again stall. The last 10 miles were without any traffic lights or stop signs, and to my somewhat surprise, it did not stall when I got home and parked the bike. Still, obviously an issue.
Scanned the codes and I got 'Lambda sensor 01' fault code no 3A2020 on the Motoscan. I went ahead and ordered a NOS O2 sensor (part no 11787716654) after taking out and verifying the original one. But then I reread this thread and decided to also inspect the vacuum/air lines going to the idle air control valve. I had done so once before, in around 2023, and found one beginning to crack. I replaced that one, but the other one looked in ok shape. Well, today that other one is VERY cracked!

View attachment 6269

Luckily, in 2023 I had bought 2 new ones, so I was able to install the new one right away.

View attachment 6270

I will still also install the new O2 sensor (can't hurt and the NOS one was only $70 as opposed to BMW's current friendly price of $450) and also install one of my 4 new mechanical timing chain tensioners. The current one (3rd one since new, the bike has 20K miles now) started to every once in a while make a faint death rattle so I figure now's the time. I bought 4 when that batch came up on Ebay for (as I recall something like) $110, so "cheap insurance" on that other common and massive problem plaguing these otherwise wonderful machines.

Will report back when I have it all back together but I am 99% confident the new idle air hose will fix the stalling issue.
Click to expand...
You will always get lambda code if engine stalls. I keep my fingers crossed you will fix the problem. I have done 3k km since ista+ adaptations, still working like new
 
Thanks Malish - good to hear your issue was solved, I can always run adaptations on Motoscan but I think I have the smoking gun. Agree the 02 sensor code probably always appears even when not the issue; I had a similar phenomenon recently with my son's Mercedes 250 GLK (diesel). It went into limp mode and threw a Mass Airflow Sensor code. Replaced the MAF only to learn that that code will appear also when there are vacuum leaks (such as with the C650) so the trouble persisted and, sure enough, an intake elbow was cracked. Once I replaced that, the problem went away and the MAF code did not come back.
 
Given I had to remove almost all the tupperware on the bike given the stalling issue, I took the opportunity to do the following:
  1. fitted a new idle air vacuum hose
  2. installed a new O2 sensor
  3. installed a used replacement oil level sensor (the old one was driving me bonkers, it would trigger the 'check oil level' warning light at random; first time it started happening I remeasured and tweaked the oil level about 7 times until I found it was always at an acceptable level and the sensor had to be at fault - the light would come on mid-ride and would not come back after cutting and restarting the ignition, sometimes for two months until it would just randomly light up again. I bought a used one off Ebay (because of course the new part from BMW costs more than a set of tires) so I hope it's now resolved
  4. installed a new timing chain tensioner, as the 'old' (maybe 7K miles) one was starting to fail
  5. checked the air filter, original one at 20K miles still pretty clean, I will replace it and the coolant and spark plugs in next year's service
  6. do the annual engine oil and filter change
Tomorrow is test drive time so will report back on whether my stalling issue (idle air vacuum hose issue) has been resolved.
 
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So the test drive was moderately successful, in that in about 50 miles of varied riding the engine did stall once when coming to a stop at a traffic light early on in the trip. However, I noticed the engine started idling better and better as the miles went by and I kind of suspect that the fuel trims, that had undoubtedly been slowly getting more and more out of whack as that idle air hose was letting more and more air, need to now adjust to the new situation. So I will continue riding as-is and hope it won't happen again. If it does, I will reset adaptations but hopefully not necessary. I must have made around 50 stops during the trip, so only 1 out of 50 stalls is ok-ish for now.
The other issue I encountered was that again the 'check oil' warning appeared. I had changed the oil and filter and put in the specified 3.1 liters. Went through the recommended 'check' procedure, and the oil level was sitting nicely halfway the 'min-max' scale, but clearly the sensor was not happy with that. I ended up filling it just to the 'max' level, meaning a full 3.5 liters, and that finally satisfied the sensor. So, for future reference, 3.5 liters is the quantity to put in, not 3.1. At least on my bike. Why BMW made this system so incredibly wonky is beyond me but now at least it runs super-strong and the timing chain is silent once more. Hopefully no issues until at least the next service.
 
Another update: I rode it some more yesterday and today - no stalling, perfectly smooth, quiet and healthy engine performance. Lately, after cold starts I could not immediately take off as the engine would hesitate, it took maybe 10 seconds to warm up a bit; that's now also gone and was likely also due to the cracked idle air hose. Really a blast to ride this bike - now starting my 9th year of ownership. Still only have 20K miles on it since I use it mostly for shorter trips.
 
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