S63TU Engine idle fluctuations and Stalling - Remedy inside!

[KLR X5M]

So I want to give you guys an update on my to an issue many people seems to be having and my investigation into these issues.

The Issue:

The specific problem of idle rpm fluctuation and stalling happens across the model spectrum of BMW that use S63tu/TU2. Seemingly comes out of nowhere, or sometime after modifications such as downpipes or tuning however it should be noted It happens on:
-F10/F12/F85/F86 etc
-Stock or modified cars( ie with catless DP or without).
-Tuned or stock.
-Cold start on or off in BM3
-ETC

I have extensively logged the issue and tried various remedies. I have ran ISTA+ tests on fuel system ( HPFP, injectors and LPFP), misfire testing etc. No errors or faults. I reset adaptations for all ECUs, re-adpated vanos system, relearned valvetronic limits, replace coils, mafs and O2s, investigated intake system leaks and replaced turbo inlet elbows and PCV, ets. Nothing helped. What I can conclusively state is that its 100% fueling related.

So What is happening?

When the motor initially starts it runs in what's called open loop fueling mode. in this state it relies on known injector characteristics and tables related to MAP, IAT, ECT to "guess" as to how the engine needs be fueled. After about 30s of running ( among other conditions) it moves to closed loop mode which leverages O2 sensors once they have heated up to provide feedback loop on fueling control.

What I have noted in the logs is when the motor initially starts, its commanding a high HPFP target. When that happens it would seem that there is a mismatch with what the ECU is expecting for injector flow and what its actually getting. If you look at the log below you can see what I mean.
When Idle begins to fluctate, its actually AFR that's bouncing around. The Bigger the AFR spike to bigger the idle dip. SFTF tries to compensate, but its not enough and eventually flutters to a stall. Once HPFP targets drop to between 1300-1700, idle stabilizes and your fine on your merry way.

What I did to fix it:

Operating under the assumption that it was fueling related, despite ISTA tests passing all components I did two things and have had rock solid idle since. My thinking here was that if open loop isn;t fueling correctly , something with the expected open loop HW characteristics was not as ECU was expecting. So I tried a couple things:

1. I reflashed the stage 2 tune with the following config options-
Cold start= Off ( note I have had this issue ongoing with both cold start on or off before)
Cold Start RPM= OEM
TMAP = OEM sensor
Manifold TMAP= OEM sensor
HPFP = Original
Immediately after flashing this idle improved dramatically.

2. Given these injectors and HPFP are known failure points, and often get clogged and cause either injector lock up or leak I ran 2 successive tanks of STP Ultra 5 in 1 Fuel system cleaner. After the first tank idle was dead smooth every start. The second tank was just to really make sure it was thoroughly clean.

Its been about 2 weeks since both those efforts and the motor is running better than ever with not 1 start with fluctuation issues and rock solid idle. I only have about 60K KM on the car, but as it known these injectors fail with >50K miles I may have bought a bit of time, but I will likely replace injectors and HPFP in the spring as a precaution.

I'll report back as weather gets colder to see if there is any remaining issues, but for now I am satisfied I have resolved it, and I am enjoying the car more than ever. Replacing those other items perhaps were not necessary in hind sight, but have helped this motor run good as new!

If anyone else wants to try to replicate my results, I suggest trying the 2 tanks of fuel system cleaner (STP ultra, Royal purple max atomizer, or techron should all work). If that doesn't do it try reflashing with the BM3 settings and see if that helps. Good luck friends and shoot me any questions.

[Garcia_f24]

Having the exact same issues, truck is at the shop getting new injectors. I'll try the settings you suggested.

[KLR X5M]

Originally Posted by Garcia_f24

Having the exact same issues, truck is at the shop getting new injectors. I'll try the settings you suggested.

Well new coded injectors will likely accomplish the same. There will be new, known injector volumes and compensation so should fuel accurately.

[bmwx5er]

Very informative post. Did you use ISTA+ to plot the fuel trims? Can you share how you went about it?

[640ijims]

IMHO, It was the Techron style stuff that dis the job. I now run a can through my F85 approximately every fourth fill up and vio'la… no more issues

[Garcia_f24]

Well, looks like the my mechanic was unable to figure out the issue. my car still seems to idle rough and have some misfires. my STFT fluctuates like crazy, I just figured out how to get LTFT to show up in bootmod3, so Im going to run a few logs.

[FirstBMWLA]

What are folks using for code scan on X5M?
on my older cars I always used my tuning app, MHD in those cases.

[KLR X5M]

Bm3, bimmerlink, ista +, or some of the foxwell or icarsoft higher end ones will do most of what you need.

[FirstBMWLA]

Originally Posted by KLR X5M

Bm3, bimmerlink, ista +, or some of the foxwell or icarsoft higher end ones will do most of what you need.

Thanks. I've used Bimmercode before. I would assume same adapter would work with Bimmerlink