[Peplano]

Hey everyone, this is my first post as I haven't seen a lot in relation to this issue, I have made some posts on /r/bmw as well, to which there was only speculation. Since about March I have been dealing with an issue where I would be cruising in higher gears (3rd, 4th, 5th) and I would get this random, yet subtle, jerk forwards. It almost feels like I slightly tapped my brakes or pushed my clutch in and rapidly released it. With this in mind, I tackled the simple things first. I replaced my spark plugs and coil packs. Immediately following that I had the issue. From there I replaced my fuel injectors and the issue seemingly was subsided. Yesterday, I cleaned my maf sensor as I was having an issue where the car kept throwing lean codes while I was up in Burlington VT. Got back, cleaned it, and the car has been running like a dream, smooth powerband, rowing gears is no problem, and overall a massive improvement on drivability. This morning, on my way to work, the jerking issue happened again for the first time in three or so weeks. Scanned for codes, got nothing, did a small pull and it was smooth. At this point, I am completely stumped. I have never gotten a HPFP code, or codes in relation to it, and thus far really haven't gotten any codes. At this point, my only solution I have in mind is to flash MHD stage 1 and see if I can replicate the issue with a fresh tune on the car. Currently, the car is on stock tune and I have the VRSF charge pipe on the car (for anything related to power modifications) aside from that its relatively stock with a BMS clutch stop, CDV valve delete from bms, and an oil change interval of 3-5k. I have also drained my trans fluid and put Liqui Moly trans fluid in. Any ideas would be great, again I haven't seen many posts directly related to this issue.

UPDATE 10/31/21: Hey guys been a few months, wanted to update with what I have done so far. I changed out my entire valve cover, and gasket recently which dramatically helped with my Lean condition STFT and LTFT's respectively. With that in mind, I tuned it as well to MHD Stage 1 and that has helped as well. I did note that my o2 sensors desperately need to be changed, and my AFR's are weird too. Could be a weird MAF error, or something likewise. Aside from that my car definitely feels better, but still some skeletons in the closet for lean codes I am getting daily. Will update afterwards considering this is becoming a prevalent issue with other n55 owners with X drive chassis.

[sav_e92]

Originally Posted by Peplano

Hey everyone, this is my first post as I haven't seen a lot in relation to this issue, I have made some posts on /r/bmw as well, to which there was only speculation. Since about March I have been dealing with an issue where I would be cruising in higher gears (3rd, 4th, 5th) and I would get this random, yet subtle, jerk forwards. It almost feels like I slightly tapped my brakes or pushed my clutch in and rapidly released it. With this in mind, I tackled the simple things first. I replaced my spark plugs and coil packs. Immediately following that I had the issue. From there I replaced my fuel injectors and the issue seemingly was subsided. Yesterday, I cleaned my maf sensor as I was having an issue where the car kept throwing lean codes while I was up in Burlington VT. Got back, cleaned it, and the car has been running like a dream, smooth powerband, rowing gears is no problem, and overall a massive improvement on drivability. This morning, on my way to work, the jerking issue happened again for the first time in three or so weeks. Scanned for codes, got nothing, did a small pull and it was smooth. At this point, I am completely stumped. I have never gotten a HPFP code, or codes in relation to it, and thus far really haven't gotten any codes. At this point, my only solution I have in mind is to flash MHD stage 1 and see if I can replicate the issue with a fresh tune on the car. Currently, the car is on stock tune and I have the VRSF charge pipe on the car (for anything related to power modifications) aside from that its relatively stock with a BMS clutch stop, CDV valve delete from bms, and an oil change interval of 3-5k. I have also drained my trans fluid and put Liqui Moly trans fluid in. Any ideas would be great, again I haven't seen many posts directly related to this issue.

I was experiencing something similar before my VANOS solenoids started to throw codes... replaced them both and the jerking went away. I have a 328xi but I believe our cars share the same vanos setup. Give that shot - or perhaps just pull yours, clean them, and replace them in alternate positions and see if it helps.

BTV is my home... glad you visited!

[whyzee125]

Damn, this is running rampant on the forums now. It's like n54 covid how quickly it's spreading lol. Mine too and I can't figure it out. I'm about to take it in.

[ValveslapAdjustment]

Originally Posted by Peplano

… and I would get this random, yet subtle, jerk forwards. It almost feels like I slightly tapped my brakes or pushed my clutch in and rapidly released it. …

That's what my car felt like when my RR tire (non-run flat) lost pressure suddenly while driving at 120km/h. I felt the jerking suddenly while driving in a straight line at 120km/h. I realized I was experiencing binding of the AWD system when the low tire pressure light illuminated 10 seconds later. Popped car in N, binding stopped, coasted to a stop. Put car in D, M1, M2 and again felt the binding.

My solution was replacing the tires because my RR tire was absolute toast. I'm wondering if your tires are mismatched or unevenly worn just enough to bind the AWD system.

'08 E92 328xi
F: 225/35R19
R: 255/30R19

[Peplano]

Hey wanted to reach out, sorry its been a late reply. I NEVER THOUGHT OF THIS!!! I just replaced the valve cover and have still experienced this! I will for sure try that immediately!

[Peplano]

Originally Posted by whyzee125

Damn, this is running rampant on the forums now. It's like n54 covid how quickly it's spreading lol. Mine too and I can't figure it out. I'm about to take it in.

Yup, I have (since the post) replaced my valve cover and I for sure took care of a vacuum leak, and the car is running great but still have this issue. Still throwing lean codes. Gonna take it somewhere to get smoke tested. Any new developments since the time I have posted this?

[Peplano]

Haven't tried this, probably will this weekend. It has been suggested a couple of times, and I had to take care of some other odds and ends on the car.