Transmission Question...(Steptronic)

[artar]

Hello! I've been lurking here for quite a while and occasionally post something but most of the time I enjoy reading and looking at everyone's photos & mods.

My wife has an '08 135i Vert w/ ~23K miles. The question is regarding the cold start (first start of the day).

When this car is started in the morning, until the engine / drivetrain reaches operating temperature, there is an interesting - and disturbing - phenomenon I've noticed. I'll drive the car up the road to the stop sign. When the car comes to a complete stop, I look both ways, etc. then release my foot off brake... the car rolls back as if it is a manual transmission car, then suddenly the driveline engages very harshly... almost like a sudden clutch release.

The car shifts fine once in motion, but this action repeats at every stop. Again, I release the foot off brake and the driveline seems to 're-engage' as if a clutch is suddenly - and abruptly - engaged. It's not quite violent in nature, but not far from it.

... as the car begins to approach operating temperature, the harshness subsides, and when fully warmed up, it does not happen.

So, my 1er friends, any ideas or concepts as to what's going on? The good news is the car has factory warranty in play so I can take it in - just trying to determine what the fark is going on here before I take it in.

Thanks to all...
Arthur

[Jeef Beef]

That shouldn't happen even if it's a cold start. You should probably have it looked at.

My mum's X3 had some transmission issues at cold start with 40,000km - sticky gears, jerky movement from stop. Lucky it was under warranty because it required a COMPLETE tranny rebuild.

[IZAGLO]

Indeed...have it looked at.... my car with STEP never does this.

[JHOOPS2]

Mine does the exact same thing. I've never thought much about it. I have right at 5,400 miles on it now.

[BrokenVert]

Is a sensor in the transmission.

The step has a decoupling feature where it essentially opens the clutch at a long stop to promote a longer life in the trans. A sensor in the fluid coupling senses when the gas is pressed, more pressure in the coupling, and reengages the transmission.

The sensor can die a slow death and when it does it doesn't operate as well as it should. It looses its sensitivity and when it does it doesn't engage immediately like it should so the car slams itself back into gear.

[BrokenVert]

Originally Posted by maxnix

Of course the hydraulic fluid is a "lifetime fill" and 15K oil change intervals are all AOK!

Yeah I don't buy that bs

[JHOOPS2]

I will have them check it out at my next scheduled service.

[Top Gon]

Mine used to do that in D mode. After I got the new software it hasn't done it since. Do you guys think it has to do with the transmission not shifting back to 1st gear when coming to a stop and then suddenly shifting back from 2nd to 1st as you try to get moving again?
Back then the way to alleviate this problem was to use Manual mode and shifting down myself. It rolled off the line smoothly that way.

[BrokenVert]

^in Sport mode...and by extension M mode the transmission doesn't decouple.

Software didn't help mine they had to replace the bum sensor

[TMR013]

Never seen this problem with mine after 20K miles. And I'm in the camp of just taking it easy till it gets to operating temp, not sitting.
I'd get it checked out. Sounds like BV might have it pegged.

[artar]

Originally Posted by maxnix

Hence one must become familiar with the concept of "operating temperature" and what the imiplications are of not waiting until it is achieved when operating the car.

Maxnix, you're a tool. What kind of answer is that? We don't abuse or run our cars hard before operating temp, or even at operating temp, let alone suggest that in my original post.


>>> Thanks to all who responded with relevant answers - BV, thank you - I'll have this checked (spot on).