[NicksN20F30]

Driving home from work last week, I was cursing at highway speeds (45-55mph) and I was about to pass someone. The engine was around 2400rpm and I stepped on it a bit to speed up to pass another car. When I did that, the car hesitated a bit and stuttered for a second and then I starting making more power and was able to pass the car in front of me.
(Sport mode, car shifting itself)

I wasn't sure what the issue was but it did happen again and I thought perhaps it was an ignition issue. I checked my records and saw it was about time to replace my spark plugs. So I did that with ngk iridium plugs gapped at 0.025 since I am modified w/ higher boost (will list modifications & etc. at the end). After I did that, the issue did not reoccur.

Driving home from work yesterday, the same issue happened again.
Hoping to get some other thoughts on where I should start looking to resolve this.

The car is a 328i xDrive (N20) 8-speed ZF Auto
FBO
BM3 stg. 2 tune
Miles: 86k

If anyone has any thoughts, had a similar experience, or could point me in the direction of where I should start looking that would be great!
I do all of my own work so I would like to get some thoughts rather than take it BMW or any other shop. If I can go about resolving the issue myself, I'd rather do that. Thanks!

[IAmATeaf]

Is the hesitation from the engine or the gearbox? My 335i sometimes does this, almost like it forgot what gear or speed the car was doing.

[_bdiddyb_]

My 335 does this too, on hard throttle, sometimes. Already replaced the LPFP, plugs and coils. Maybe boost leak, maybe bad gas, or could be the HPFP crashing.

[NicksN20F30]

Originally Posted by IAmATeaf

Is the hesitation from the engine or the gearbox? My 335i sometimes does this, almost like it forgot what gear or speed the car was doing.

It definitely seems like it's coming from the engine rather than the gear box. Because right before it stutters, the car picks up just a little bit, stutters, then does what it's suppose to. No cel's or nothing either.

[NicksN20F30]

Originally Posted by _bdiddyb_

My 335 does this too, on hard throttle, sometimes. Already replaced the LPFP, plugs and coils. Maybe boost leak, maybe bad gas, or could be the HPFP crashing.

Yeah it's inconsistent. It doesn't happen every time but sometimes for sure. Highly doubt it's my gas, could be coils. I hope it isn't HPFP lol

[IAmATeaf]

I think in my case it’s the gearbox where it’s in too high a gear, it then drops a cog or two and you’re away. Doesn’t happen too often but when it does the ends up lurching forward.

[upsidedownfunnel]

Have you ever changed your transmission fliud? If you're modded and driving hard a lot, at 86k miles, it might benefit from a fluid change. Even if BMW claims it's a "lifetime fluid", there's no such thing.

[NicksN20F30]

Originally Posted by upsidedownfunnel

Have you ever changed your transmission fliud? If you're modded and driving hard a lot, at 86k miles, it might benefit from a fluid change. Even if BMW claims it's a "lifetime fluid", there's no such thing.

I have not changed the fluid. From time to time I do drive the car hard but not constantly. I also agree with you about "lifetime" fluid. I don't think any fluid is made to be used for the entire life of the car.

However I have heard of people changing fluids in these cars, specifically the trans fluid, and that's when problems end up occurring that weren't present before.

What's happening with the stuttering isn't making me think there is a problem transmission wise but rather something with the engine. I'll look into though. My thought was that if I take this car to 100k miles, at that point I would change the trans fluid regardless. But maybe it would be wise considering I am modified.

[upsidedownfunnel]

Originally Posted by NicksN20F30

I have not changed the fluid. From time to time I do drive the car hard but not constantly. I also agree with you about "lifetime" fluid. I don't think any fluid is made to be used for the entire life of the car.

However I have heard of people changing fluids in these cars, specifically the trans fluid, and that's when problems end up occurring that weren't present before.

What's happening with the stuttering isn't making me think there is a problem transmission wise but rather something with the engine. I'll look into though. My thought was that if I take this car to 100k miles, at that point I would change the trans fluid regardless. But maybe it would be wise considering I am modified.

If you feel it's not the transmission, you should trust your gut. It really could be anything. Perhaps a boost leak, or pre detonation due to bad gasoline?, or dirty injectors. Maybe plug in a code reader to see if you have any codes.

[CrumbyButter]

Spark plugs? Ignition coils?

[NicksN20F30]

Update 11/25:

I mean to update before this but I noticed the stuttering more frequently and it felt it was coming from the transmission. After doing some research I thought to believe it was the trans fluid as the symptoms for bad fluid where what I was experiencing.

Today I had taken my car to a shop that works primarily on German vehicles to have a transmission fluid change. Mechanic said that the old fluid was dirty and that I should notice a change in performance.

Got it back about and hour ago and drove it home. Night and day difference.

Stuttering is gone, rough shifts gone, completely smooth now and how it should be.


I was leaning against something transmission related because I know how well the ZF transmissions in these cars and many others perform. I also didn't think the fluid needed to be changed because of BMW's claim that it's a "lifetime fluid". I didn't fully believe it to begin with but from other BMW owners experience, they have claimed they've made it to 100k miles before changing.

Car is running smooth again and performing waaaay better. I definitely should have done this long before now.

Also for anyone else, ZF recommends every 50k miles for a fluid change if I'm not mistaken. One more thing is if you want/ need this done, make sure you say transmission fluid CHANGE and not flush. ZF states that the process of a transmission flush can cause damage.

Hope this helps anyone else having a similar experience and shoutout to anyone who said transmission to begin with lol.