Surging and bucking off the line???!!!

[saildoc]

My car is still doing it. Has the DCT. Cold starts are the worse. Like driving a bucking broncho with lurching and surging. Service dept says it is normal for the car to do that. I have read many posts, some have pointed out that it is due to trottle sensitivity. If so why is it an intermittant problem? Also upshifting to 2nd doesn't make it go away. Some days, I don't feel it at all. This has not been much fun-love the car otherwise... Any thoughts? Thanks

[Jeff_DML]

I get it sometimes get it too with my 6MT on normal throttle setting, seems to happen only when the engine is cold for me.

[ersin]

I don't have DCT, but I would suggest driving it like grandma until it warms up. Even the 6MT is a bit clunky while cold. The '02 SMG M3 has was like this too. I think it's just one of quirky things about a car like this.


Cheers.

[BigHat]

The engine runs rough until warm for emission control reasons. I have a DCT-equipped car too and it's never more than a 30 second problem for me. I usually start it, let it sit for 20 secs, tap the throttle to engage the "walking" pace forward roll pulling out of my parking spot. By the time I'm clear of my spot I can select 2nd without it bucking, etc.

I'm actually quite impressed by how quickly the oil temp comes up in this car. In my 650 I could commute most of a 5 trip before oil temp even came off the peg.

[kouhii]

I am not sure if this is the same. Try to shift before 2k rpm when the engine is cold.
It happens when you depress the pedal a little hard and the rpm quickly goes to somewhere between ~2k and 3k rpm then you hold it there it will jerk the car back and forth, try not to set throttle response to SPORT PLUS when engine is cold or be very easy on the gas pedal.

[quality_sound]

Mine only does it if I don't let the engine warm up until the RPMs drop. Once they drop I never have a problem.

[C17MooseDriver]

I get in in my 6mt if the engine is cold. But in only lasts for a few minutes with low throttle input. After that, it works fine.

[Reedomn]

Originally Posted by Jeff_DML

I get it sometimes get it too with my 6MT on normal throttle setting, seems to happen only when the engine is cold for me.

+1...

[Montoya]

OK- those of you from the old boards remember UMP... The E46 SMG would do this too. UMP, who is a pretty good track driver finally figured it out. So here is the solution:

When it happens, take you foot completely off the throttle- not lifting, not touching, but completely off. The bucking stops, start accelerating slowly, problem solved.

Why? Once the bucking oscillations start, your foot on the throttle makes it worse because even though you think you are lifting each oscillation pushes your weight forward which is just enough to push your foot into the throttle pedal (even when lifting) to keep the whole bucking and surging thing to continue.

The key is your foot completely off the pedal. Try it, it has worked on both my E46 and E92. It just takes a second, it stops and you are smoothly on your way again.

And yes, it will help if you keep the power button off so the throttle sensitivity is easier to modulate, but it can happen either way.

[quality_sound]

Didn't the E46 have a throttle cable though? Ther E9x had a cableless throttle and the ECU smooths small fluctuations in input as a mileage improving measure.

[Montoya]

Originally Posted by quality_sound

Didn't the E46 have a throttle cable though? Ther E9x had a cableless throttle and the ECU smooths small fluctuations in input as a mileage improving measure.

I don't think it did, I'm pretty sure it also had a drive by wire system- how else would the power button work?

Whether or not the ECU adapts is irrelevant regarding low speed bucking and surging, the principle cause is your foot on the pedal and your weight being thrown forward, causing an oscillation to continue.

Look, it's like when data acquisition first came out on race cars. Mario came into the pits and swore up and down that at Indy he was flat out through turn one. The engineers looked at the data and said, "No Mario, the data doesn't lie, you are lifting slightly". So Mario took the car out again, but this time he put his left foot on top of his right foot to keep the pedal down. When he came back in they confirmed that this time it was in fact 'flat out'. He scared himself silly though to prove his point.

My point is.... that while you think you are lifting, the very fact your weight is shifting makes it very hard to actually prevent the modulations that enhance and extended the bucking. The only way to stop it, is to completely remove your foot from the accelerator pedal.

[Krozi]

Mine does it in the morning, especially after hitting a small bump or if I am not REALLY easy on the throttle.....only does it once though..after that its smoooth

[quality_sound]

Originally Posted by Montoya

I don't think it did, I'm pretty sure it also had a drive by wire system- how else would the power button work?

The same way cruise works on a cable throttle car.

Whether or not the ECU adapts is irrelevant regarding low speed bucking and surging, the principle cause is your foot on the pedal and your weight being thrown forward, causing an oscillation to continue.

I know what you're saying but every drive-by-wire car I can think of those specific oscillations are ignored by the ECU. The difference between this and your Andretti example are the frequency.

[m3convertdriver]

happened to me today in NYC around about 500 people... took it out of the garage, wasnt trying to peel off or anything like that. did the bucking bronco slightly embarissing as i think everyone around me thought i was learning how to drive stick.. actually, was pretty funny.

[eeeboy]

start in 2nd gear until warm...done!!!

[Finnegan]

Good info on correcting the issue once it starts. The drive by wire system on this car seems to exacerbate this issue. 6MT or DCT it seems relatively easy to get things to buck on heavy throttle even when warmed up (more so of course when cold). Even a hard start with the DCT when the car is fully warm can result in you feeling like a 16 year old driving your first manual--which is embarrassing and annoying. The E86 (S54) isn't nearly as picky despite being drive by wire...so it's something about this electronic system that is a bit "off" IMO.

Specifically regarding the cold engine roughness and bucking, just let the engine warm up enough to get out of the cat warmup cycle. A couple minutes max and you're ready to go.

[ilidon]

it's normal when its cold. it happens all the time when i don't warm up the engine for a minute or two.

[Montoya]

Originally Posted by quality_sound

The same way cruise works on a cable throttle car.



I know what you're saying but every drive-by-wire car I can think of those specific oscillations are ignored by the ECU. The difference between this and your Andretti example are the frequency.

The E46 M3 had 6 individual throttle bodies controlled by a drive by wire system (no throttle cable). FYI

I don't think you got the point of my example. The point is: What you think you are doing and what is actually being transmitted to the throttle can be very different. These are not little throttle oscillations that get damped by the ECU.

[quality_sound]

No, I get what you're saying. I'm disagreeing. Either way it's a moot point because if the ECU is supposed to damp the oscillations, it doesn't appear to do it very well in this case. But for the record, I still don't think the driver's foot is moving enough to be the cause.

[JCtx]

Originally Posted by Montoya

The E46 M3 had 6 individual throttle bodies controlled by a drive by wire system

The reason it bucks when cold IMO is the lack of a 'Mass Air Flow' (aka MAF) sensor, due to the individual throttle bodies (TBs). In open-loop mode, ECU can't measure air flow like a system with a MAF, so until the O2 sensors come on board, the bucking stops. When cold, all cars operate on maps, but with a MAF sensor, fueling is more accurate. It's the nature of the beast. If you go easy on the throttle but not too hard or too easy, it's almost nonexistent; just experiment with the throttle to find the sweet spot. And I have the throttle on 'sport' all the time. Take care gang.

[ASGM3]

just take it easy till the lil red needle is in d center and then enjoy

[Peter B]

I get it too with DCT - it happens randomly but more frequently from cold starts.