Stutter when driving off with DCT on cold starts

carabuser

Lieutenant
Oct 2, 2019
870
1
765
0
UK
Ride
Z4 35i & 335i
I've been having an issue when first pulling away on cold starts and wanted to know if anyone else has had this.

When I first let off the brake and let the car creep forwards the revs will dip a lot and the car labours for a second before pulling away normally, it feels close to stalling sometimes. I've linked to a log of the behaviour with a marker placed where the drive-off occurs. It will keep doing this to a lesser degree for the first couple of minutes of driving then after that it's absolutely fine.

It only happens when the engine is cold on the first start of the day. Outside temps here are about 5-10C so not anything crazy cold.

Some things I've already considered and ruled out:
DCT software: Does it with the latest Z4 35i software and also the 35is software.
DCT Adaptions: I ran through all the adaption routines in ISTA following all instructions and there's no change
Fluid leak: Transmission has no leaks, the sump and gasket were replaced by BMW 1 year ago with fresh fluid.
Parking brake sticking: Does it even when car is left without parking brake disengaged (It's an e-brake on the Z4)
Engine adaptions: All reset with MHD, no change
Engine tune: flashed back to stock with a full WinKFP write and no change.
Parts: Car has relatively new injectors (index 12), HPFP, LPFP and coils.

Log here: https://datazap.me/u/rich/dct-cold-first-gear-engagement?log=0&data=3-14-22&mark=276

Some things I'm suspicious of:
Spark plugs: It's hard to pinpoint exactly when this started but last summer I changed the plugs to NGK 5992 , gapped them to 0.022". I've rechecked the gaps on all of them since and everything is spot on, no fouling on the plugs or anything suspicious.
Downpipes: I also swapped to some VRSF catless pipes at the same time as the plug swap. Could this possibly make a difference? I'm certain I've got no leaks and surely during cold start the car runs in open loop so O2 senors can't be blamed?

Any suggestions are welcome. It's not causing any serious problems for me, but I want to figure it out in case it gets worse.

I'd also really appreciate if anyone else could just grab a log of their DCT pulling away on the first start of the day. Would give me something to compare.
 

derekgates

Lieutenant
Feb 23, 2018
740
375
0
NW FL
derekgates.us
Ride
2011 335is
Sheesh I have similar problems with my 335is but I attribute it to turbo issues. If/when I get it in a driving state I will try to get some logs.

Impressive research and notes here. Wish I could help more!
 
  • Like
Reactions: carabuser

JohnDaviz

Lieutenant
Jan 6, 2019
863
577
0
Ride
335i E92 DCT
i have the exact same thing with reverse during winter when its cold. But its only the first time i set it to reverse.

Thought it was tuning related but never considered it serious. But my pan is leaking also :D
 
  • Like
Reactions: carabuser

carabuser

Lieutenant
Oct 2, 2019
870
1
765
0
UK
Ride
Z4 35i & 335i
Really strange that you both have it too. I don't remember it happening as much in the past but it only happens in winter.

Hopefully we'll get some more data points off others.
 

aus335iguy

Colonel
Nov 18, 2017
2,248
803
0
Down under
Ride
335i DCT 2009
Could it be one or more of the brakes binding?

You may have tried to maybe jack the car up when cold and see if the wheels spin freely. Remember to put the car in neutral
 

JohnDaviz

Lieutenant
Jan 6, 2019
863
577
0
Ride
335i E92 DCT
On my car it is not brake related. I would bet my money on clutch pressure is off during that first shift to reverse on my car.

On my car the oil is 10 years old. So conditions going to one extreme like cold and therefore thick oil could have an influence on pressure regulation and general behavior during these first seconds.
 

aus335iguy

Colonel
Nov 18, 2017
2,248
803
0
Down under
Ride
335i DCT 2009
Well if your seals are leaking and it’s exhibiting that sort of behaviour then an oil change and seal replacement is likely a fix for you. I’m in a warmer climate and haven’t seen this sort of thing so you could be right
 

carabuser

Lieutenant
Oct 2, 2019
870
1
765
0
UK
Ride
Z4 35i & 335i
OK, think I solved it. I was running too lean. I went back to stock fuel target in the load/rpm range of the drive-off and everything is fine again. I had leaned out the fuel target after installing downpipes to see if it helped reduce the smell.

I don't know why flashing back to the stock tune didn't show a fix but maybe that was because the car was sat with the parking brake engaged for a long time.
 
  • Like
Reactions: derekgates

JohnDaviz

Lieutenant
Jan 6, 2019
863
577
0
Ride
335i E92 DCT
Interesting. Stock is 14.643 in 335iPPK and my tune has 14.671 Target AFR in that range.

What are your values?