E85-M54 Idle Issue when Cold

[sim_mat]

I'd like to know if this could be caused by a Vanos failure?
https://youtu.be/QlL_KLE8Iqs

The issue in the video is one of the more severe occurrences. It's more common that during cold idle, the engine just dies. I can restart no problem but it might die again after a minute of idling. Once the car is warm, I don't notice the problem.

In these severe cases, it will provide a host of fault codes that I think result mostly from the engine dieing. Not necessarily the root cause.

Based on other posts, I have replaced the throttle body, the crankshaft position sensor, and cleaned the idle air control valve. I reset the adaptations, etc. None of those fixed the problem.

I have the Vanos parts to do a rebuild but before I tear into that, I'd like to see if anyone else has had a similar experience and fixed it.

 

[bigwinn]

I’d say not

Happy to stand corrected

Vanos issues in my experience usually don’t throw codes and lights like that

To me that looks like DME issues- what codes does it show when read?

 

[sim_mat]

I’d say not

You might be correct. I'm happy to try to diagnose that but I'm not sure how.

I've seen:
3C1D DME: Crankshaft Sensor Signal
2830 DME: DME Self-Test checksum
2796 DME: Throttle: Adaptation Values Incorrect
P0335
P1632
P16A1 Internal Control Module memory checksum error in application software
28B2 DME: Speed Limitation: Reset
27A1 DME: Throttle Starting Test
93E7 SM: Undervoltage
P1634 Throttle Valve adaptation valve, spring test failed
P16A3 Internal Control Module Non-Volatile memory error
27A1 DME: Throttle Starting Test

If you look in the log file, you can see that just before the engine dies, the MAF reading is half the previous reading, and about 600ms later the RPM changes from 1166 to 0 instantly. About 6 seconds later, the MAF reading goes to 0 as well.



I do not know what this would indicate but it doesn't seem normal.

I'll take whatever advice you have to offer.

Thanks!

 

[Street]

I take it you’ve unplugged the MAF as a test so the engine runs on a default map?

 

[bigwinn]

I’d deffo do simple free stuff first- as street says do the mag thing

The risk is you can end up chucking money at stuff that isn’t the issue too… it may be dme but it could be something different

Isolate the codes immediately during or after the event

What engine size is it and location? To rule the dme out you’d need to swap it over and delink the ews, some members have the software to do that

 

[sim_mat]

Thank you. Is there a technique for forcing the default fuel map other than unplugging the MAF sensor? If I unplug the MAF, it won't start.

This is the 3.0 in a 2005 Z4. Scanner shows ECU # 6937791

I'll try to do further work on the codes and when they occur.

 

[enuff_zed]

So maf unplugged it won’t even start?
What if you start it then unplug the maf?
Combined with your codes it does seem to suggest a DME issue as if it cannot see the maf it will usually still run.
Could perhaps be an issue with the potentiometers in the throttle body?

 

[sim_mat]

What if you start it then unplug the maf?

It will still run. I will get some fault codes, though it's difficult to determine if that's the cause.
For example, I just ran this "test" starting with no logged codes:
-Start Engine w/ MAF plugged in
-Unplugged MAF and allowed engine to idle for a minute
-Plugged MAF back in
-Turned Engine Off
-Checked codes
In the DME, I found 28B2 (DME: Speed Limitation: Reset) with SAE Code P16C3.
In the DSC, I found 5E19 (ABS-DSC: CAN data error from DME/DDE.)
I could see in the log that the "Air-mass Flow" went from 30.84 to 0 while I had it unplugged then back to 26.97 when plugged back in.

I restarted the engine to find it was "surging" like it does after this issue. (Sorry, I do not know the proper term for this surging condition)
A new code appeared: 2830 (DME: DME self test checksum) with SAE Code P16A1

I tried starting the engine again with the MAF unplugged and logged: 2869 (DME: DME self test: RAM check faulty) with P16A3

I can reset all these and get back to a running state but the stall

Could perhaps be an issue with the potentiometers in the throttle body?

That was my first inclination and I replaced the throttle body with no success.

 

[Motionblurrr]

What does your air filter look like?

Have you ever cleaned your MAF sensor with a dedicated MAF sensor cleaner spray?

Is your battery in great condition with no dead cells? Alternator?

I'm poking at the easy stuff first. Sometimes, it could be a combination of things that make that happen. A failed DME is costly and not that common IIRC.

My money's on the air portion of your car's set up. I suspect a vacuum leak, bad/dirty MAF.

 

[sim_mat]

The air filter is fine. I have taken apart most of the parts leading to the intake and don't see anything that could be a vacuum leak but who knows. I don't have a smoke machine.

I've ordered a new MAF to eliminate that possibility.

I wish there were a way rule out the DME. I'm concerned that everyone says the unplugging the MAF should force a default fuel map but my car won't start if it's unplugged. And in the data log, I see some suspiciously round values from the MAF that don't look live.