E38 stuck in idle fuel trim cell after cold start

[TRStech]

Hi all,

Im struggeling with the ECUs behavior after cold start. I retarded catalyst heating spark to get quicker catalyst light off. Under idle and also under idle with "simulated" driving by increasing idle this works pretty OK and Im close to the target Im aiming for. Unfortunately this looks far different when car is actually driven.

I have to pass a emissions test what includes a drive @15kph with a duration of 8s and starts 11s after cranking. After that, ideling 21s at stopped car, then accelarting to 15kph in 1st and 30kph in 2nd, then drive for 24s. Goal is to get the catalyst working (what means post O2 signals constant) before the second part (30kph run).

The ECU somehow is struggeling to keep spark constant under driving conditions. In the atached log you see the spark massively oscilating at towards the end of the first 15kph part. At this point the car also starts bucking, first slightly then getting more and more massive. I logged all avalable spark adjustment parameters but non is actualy showing the fluctuations that can be seen in the commanded spark.

What I already noticed:
-the car stays in FTC 14 during the 15kph run, what, as far as I know, is a idle FTC and no driving FTC -> is this normal?
-it seems to start when rpm is getting arround desired idle rpm
-desired idle is hire then what the different tables where its set would show
-After depressing cluth, thers also a spark oscilation during entering idle rpm, I expect this beeing a effect of adaptive idle since it starts right after adaptiv idle VSS is achieved -> further ideas?

I already played with the spark smoothing tables and also turned them off completely. Turning off didnt help, made it even worse. With warm enigine I tuned out pretty much any bucking even though I have a pretty high drivetrain backlash. But at cold start it somehow seems to freak out.

I then tried to disable clunk reduction spark. It improfed on first sight, but I cant say for sure yet since I didnt had chance to test on a full cold start since I have to wait for the colldown at the moment.

EDIT: One further question: Has anyone an idea what is limiting idle spark to -7? Looking at the cat lightoff spark retard it should be even more retarded, but it seems somehow it is blocked at -7 idle spark.

Thanks!

20210703_V0.64.hpl
Camaro_LS3_modifiziert_V0.64.hpt