[Drpoomanchu]

could the diverter valve being sticking or not functioning properly. possibly the diverter valve sticking open while in transition from on boost to vacuum after lifting throttle ?

[MegaMatt3]

Thanks Xutvjet for your detailed response. I'll take your suggestions to the dealer when I take it back next week for them to re-examine the issue.

One thing to note: I may have been misleading when talking low RPM's. It's not typical for me to drive or shift at sub-2000. I had a manual Civic for 10 years and a manual Acura for another 6 years after that, neither of which had the silly shift suggestion on the dash. I agree, it's generally too low - I consider it a feature for fuel saving and not practical for daily driving. I'm much more comfortable shifting between 2500 and 3000, which is the way I'd always driven before I had my car telling me when to shift. So I don't follow the suggestions from the car. Point is, I think I drive it normally for a manual, not cruising in too tall a gear and not shifting too soon. But I'll make note of what I'm doing anyway to be sure.

The most recent time I noticed this behavior was in third gear, coming off throttle, somewhere between 2000 and 2500. I think that's a normal cruising engine speed, maybe on the lower end, but I was decelerating in traffic.

I'd been shopping for a while at this local, no-name gas station right by my house, filling with 93. Someone else earlier in the thread also suggested switching gas stations, so I haven't gone back there since, opting instead for name brand places like Shell and BP. It's only been a week (2 fill ups), but I haven't noticed an improvement yet.

I'll post an update when I hear the next round of feedback from the dealer.

[MegaMatt3]

Originally Posted by Drpoomanchu

could the diverter valve being sticking or not functioning properly. possibly the diverter valve sticking open while in transition from on boost to vacuum after lifting throttle ?

I know very little about car mechanics, so I'll leave someone else to chime in if they think that's plausible. But I can certainly posit it to the dealer. On the surface it sounds like something that could be causing this symptom.

Again, the dealer did check it out once before, but I hadn't explained the problem very well so they may not have checked the right things.

[Drpoomanchu]

Originally Posted by MegaMatt3

I know very little about car mechanics, so I'll leave someone else to chime in if they think that's plausible. But I can certainly posit it to the dealer. On the surface it sounds like something that could be causing this symptom.

Again, the dealer did check it out once before, but I hadn't explained the problem very well so they may not have checked the right things.

Yea, i just threw it out there. There are more knowledgable people on here than myself but didn't see that mentioned. I know with boosted cars there can be issues related to recirculating and non-recirculating systems where if the blow-off valve or possibly the diverter valve not adjusted properly or malfunctioning can cause a rich condition coming out of boost to vacuum and can cause symptoms of stumbling or stalling . Im just not too well versed in BMW platforms. Im sure someone will chime in if it could be relevant. Good luck

[XutvJet]

MegaMatt3,

You may be a bit happy, I believe I may have felt what you're talking about. I too have a 2016 M235 6MT with around 8,000 miles. Yesterday, while driving in DTC Off mode, I experienced a rapid and very quick thud-thud-thud immediately when letting off the throttle from ~2,000rpms in 5th gear coming up to a stop light, just before I was going to shift into neutral. The "thud" could be felt through the steering wheel and seat, but my wife didn't seem to notice. The tach didn't show anything. It almost felt like when you leave the car in gear coming to a stop and the motor is threatening to stall out. When it happened, I thought that this may be what you're talking about. I also think I may have felt it before once or twice in the summer.

Last night I went for a long drive and put the car under all sorts of load situations and monitored parameters via my BT OBDII scanner. I couldn't get it to do it.

These were the conditions when the car flaked out yesterday:

1) The car hadn't been driven in 24 hours thus a stone cold motor. When it happened, the car had only been driven for 6 to 7 minutes was not up to operating temp yet. Per my ODBII scanner, it takes a solid 10 minutes of driving to get the motor up to temp.
2) A few minutes before it happened, I had turned on the A/C.
3) Conditions at the time were low 70s and humid.
4) The car was under absolutely no boost.
5) I always shop at the same BP station and run 93 octane.
6) No codes were stored.
7) The car has no performance mods.

I have a hard time believing it's any sort of turbo component issue because I wasn't using boost at the time. I don't think it would be an injector because they're not adding fuel in off-throttle situations. It wouldn't be a coil or misfire issue because although the coils are always firing, cylinders aren't getting fuel in off throttle situations until around 1100rpms (to maintain idle). It's not a clutch issue because I wasn't touching the clutch at the time.

Right now I'm thinking it's some wonky random tuning issue and possibly related to the A/C compressor cycling at certain moment of time which causes a momentary flake out of the DME.

Do you routinely run the A/C? What ambient conditions do you typically drive in? I'll keep you posted as I monitor this.