[N52UNED]

This has happened only twice in the past 3 months. '07 328i auto. Daily driver (at least driven more day than not ~ 1k miles per mo.) 40,500 miles now.

I'll be stopped at a traffic light ... while the brake pedal is depressed, the car will lurch forward like someone bumper tapped me. (automatic climate control is on - AC running)

The first time I saw my RPM's drop a couple hundred for a split and then back up to normal. It felt very slight. My passenger didn't feel or notice a thing. It happened to me again today .. but was a more pronounced lurch. I didn't notice my RPM's, but I believe the engine sounded different than regular idle but I wasn't paying much attention and had music playing.

There's no CEL

Both times I had just come from the highway (if that matters). Both time acceleration after the stop isn't an issue. The car slows and brakes as normal.

Again, this has only happened twice so I cannot plan or replicate it. Just wondering if this is a BMW quirk or something more.

I've researched this but I can't seem to find a definitive answer, as many posts online have other issues like braking involved. I've also read that it's a normal quirk, torque converter, needs reprogramming (but for when there is also issues when pulling away).

I haven't tried a transmission reset (holding gas pedal down). I did this when I installed my 3IM and BPC tune ... but not since if that matters.

Thanks ahead of time.

[rjahl]

Originally Posted by N52UNED

This has happened only twice in the past 3 months. '07 328i auto. Daily driver (at least driven more day than not ~ 1k miles per mo.) 40,500 miles now.

I'll be stopped at a traffic light ... while the brake pedal is depressed, the car will lurch forward like someone bumper tapped me. (automatic climate control is on - AC running)

The first time I saw my RPM's drop a couple hundred for a split and then back up to normal. It felt very slight. My passenger didn't feel or notice a thing. It happened to me again today .. but was a more pronounced lurch. I didn't notice my RPM's, but I believe the engine sounded different than regular idle but I wasn't paying much attention and had music playing.

There's no CEL

Both times I had just come from the highway (if that matters). Both time acceleration after the stop isn't an issue. The car slows and brakes as normal.

Again, this has only happened twice so I cannot plan or replicate it. Just wondering if this is a BMW quirk or something more.

I've researched this but I can't seem to find a definitive answer, as many posts online have other issues like braking involved. I've also read that it's a normal quirk, torque converter, needs reprogramming (but for when there is also issues when pulling away).

I haven't tried a transmission reset (holding gas pedal down). I did this when I installed my 3IM and BPC tune ... but not since if that matters.

Thanks ahead of time.

While stopped, try bumping the gear shift between first and second, manual mode. You will get a "bump" when the gearbox shifts, does it feel the same?

If so, the random bump you are feeling is probably just the TCU logic taking first gear after you stopped. Sometimes there is newer TCU software to help resolve this.

[N52UNED]

Originally Posted by rjahl

While stopped, try bumping the gear shift between first and second, manual mode. You will get a "bump" when the gearbox shifts, does it feel the same?

If so, the random bump you are feeling is probably just the TCU logic taking first gear after you stopped. Sometimes there is newer TCU software to help resolve this.

Thanks for the input!

I've tried what you suggested ... while stopped (brake depressed) M-shifting 1-2 ... I don't get any lurch ... nothing actually. However it does feel like going from Park to Drive. Is this what you mean?

... I've read about that update ... wasn't sure if this was a case for that.

[N52UNED]

Originally Posted by BimmerGeeks

Update your transmission & disable NIC & see if it helps.

would a 330i transmission update help that? I've been dragging my feet on doing that.

[N52UNED]

Originally Posted by BimmerGeeks

Are you a GM trans?

I'd really only recommend the 330i flash if you have 3 stage manifold & a tune to compliment it.

Yup GM. Yes I have the 3IM and running a BPC tune.

[BOOF-M3]

I have owned three BMW's of the Automatic variety and all have had movements of doing the lurch dance while stopped at a light. Almost as if the car is burping. My sense has always been that it was a gas related issue as opposed to transmission. But it has been so infrequent and only momentary that i didn't pay too much attention to it. I will certainly follow your thread and see where this leads.

[N52UNED]

Originally Posted by BOOF-M3

I have owned three BMW's of the Automatic variety and all have had movements of doing the lurch dance while stopped at a light. Almost as if the car is burping. My sense has always been that it was a gas related issue as opposed to transmission. But it has been so infrequent and only momentary that i didn't pay too much attention to it. I will certainly follow your thread and see where this leads.

Yes, it is rather infrequent. This was only the second time in the past few months. I've had the car since last fall ... about 11k miles. Both times were like a blip.

But with that ... I figured I should be proactive and research what's going on. I started this thread to find out if it's something I should be concerned about that I should address asap (ie. torque converter/some other trans issue or some mechanical issue). Have read about the trans update, but unlike others who complained about this issue ... I don't have any lag/hesitation when I go after the stop. It's a strange lurch after I've been at a light for about a minute or so ... then right back to normal.



I'm not sure about the gas ... but I can't rule it out. I typically fill up at 2 gas stations in town ... both Shell. The vast majority of the time I use 93 octane. Every Once in awhile I'll top off with 89 but never more than half a tank (only if I'm down about a third and am about to use up most of a tank during a trip that day). Only once have I put in "regular" but that was just 5 gals when I was getting gas for my yard equipment.


I'm guessing that since it happens so infrequently; it will be a while before I'll know if a trans flash fixed it.

[BOOF-M3]

Yes, certainly not something that is going to be easy to diagnose and thankfully since it's a very rare occurrence as opposed to an every day blip. I had always assumed fuel, fuel injectors, coils, plugs or just a momentary ECU issue. I had not thought of the transmission as cause and affect. You always post thought provoking questions and answers. This one is no different. Carry on Chaz