[Liandri]

Just wanted to necro in and say, I have this exact behavior going on in my 2016 m235i w/23k. It only happens when the car sits for a long time, such as overnight. Does not happen on restarts, and is definitely not dependant on temperature.

It has progressed in 2 stages. The first stage (all stock car) was a fast rev up-rev down approx 300rpm in either direction directly after startup and only lasted 3 seconds or less and stabilized. If i sounded it out in text it would go "vroom-vroom-vroom-vroom-vroom-vroom-vroooooooooooooooooooooooooooom" lol.

The second stage is the one in the video above, to a T. Drops a lot of RPM in a big stumble and then comes back up, only once, and idle stabilizes. That video is exactly how it happens now. The difference is I have installed charge pipes and an AA FMIC (stock tune). I can't and won't say the two are related, but it didn't do it like this before the charge pipe-IC install. There are a million reasons it could have changed behavior so not reading into it too much, will recheck all connections, but considering it the same problem unrelated to CP/IC. I also put BMW fuel system cleaner in a few tanks ago.

I have always used Shell 93 in this car, going on about 6k miles so I doubt it has anything to do with that. Has anyone definitively found the cause? It seems to happen every cold start where the car has been sitting overnight, and I'd like to know if it has anything to do with the HPFP losing prime over long periods. Or possibly vanos actuators losing oil prime. I'm not going to replace any parts for now and see if it gets worse. I'll check the charge pipe connections, and I'll be flashing MHD tune sometime this summer and will see if that changes it at all

[SOLOMEK]

Old school stab... fuel filter? Injectors? Spark plugs? Air filter?

at 70K, it's time!

[Liandri]

Originally Posted by SOLOMEK

Old school stab... fuel filter? Injectors? Spark plugs? Air filter?

at 70K, it's time!

He's at 70k, but I'm at 23k with the same issue. I just checked and looks like there is a filter or strainer integrated into the hpfp, so not serviceable. I changed spark plugs last year with OEM so will assume those are still good. I ordered OEM Delphi coilpacks as something to try, I ran across a few posts from other threads where guys shotgunned coils and plugs and fixed the issue. Given BMW history with coilpacks it's not a bad idea to try ($166 on rockauto for 6). I'll report back when I put those in, worst case I have spare coils

[kthor703]

Originally Posted by Liandri

He's at 70k, but I'm at 23k with the same issue. I just checked and looks like there is a filter or strainer integrated into the hpfp, so not serviceable. I changed spark plugs last year with OEM so will assume those are still good. I ordered OEM Delphi coilpacks as something to try, I ran across a few posts from other threads where guys shotgunned coils and plugs and fixed the issue. Given BMW history with coilpacks it's not a bad idea to try ($166 on rockauto for 6). I'll report back when I put those in, worst case I have spare coils

Please do. Have some minor cold start stumbles and haven't changed the coil packs yet. About 45k on mine.

[Liandri]

Originally Posted by kthor703

Please do. Have some minor cold start stumbles and haven't changed the coil packs yet. About 45k on mine.

No change with the new coilpacks. I had put new plugs in before winter storage so that rules both out. I also cleaned the MAF with CRC mass airflow cleaner, also no effect. I started logging for the issue and found:

High side fuel rail pressure is stable @2500psi during the event
Low side fuel is stable @ 200psi at all times
Front AF sensor voltage is stable at all times

High side rail pressure was about 127psi after sitting for 8 hours. Immediately jumped to 2500psi and held on startup. I'm not sure what bleedoff is supposed to be but I don't feel the HPFP is the problem given the data showing full presure and no real deviation during the event

The car starts and revs up normally just like OP's video, then crashes and stumbles before reving up again and normalizing. The fact that it runs fine for 1-2 seconds then falls makes me think an injector isnt leaking rail gas into a cylinder overnight. I would expect something out the tailpipe or a more violent stumble if that were the case, would expect the cylinder to be flooded. I will try and log other values such as MAF in the coming days. I'll probably try unplugging the MAF as well. If anyone else is making progress on this, please let me know

[2Faded35i]

Same exact issue...2016 m235i mt 73k...Started after I installed my intake, which is the only mod I hv on the car.

[Liandri]

Originally Posted by 2Faded35i

Same exact issue...2016 m235i mt 73k...Started after I installed my intake, which is the only mod I hv on the car.

I can't be completely certain, but I have a sneaking feeling mine got worse (to exactly what's in the video) after the charge pipe and intercooler install. Car already had AA downpipe. I reset engine adaptations and learned data this morning after I parked the car, so I'll see later if that has any effect on the issue. I halfway wonder if flash tuning might fix it, but doubtful. I wasn't going to get into this right now but now my curiosity is killing me

[shocksim]

I had this same problem, at one point got a "Bank 1 Too Rich" CEL, went through a lot of troubleshooting. New colder spark plugs, cleaned air filter, cleaned maf filter, traced the intake for a vacuum leak, remounted the intake, and updated/reflashed a couple times.

Car would be fine til it started to settle into the tune and then would idle really rough every cold start and i would say every other cold start it would stall out. I'm only at 30K miles too.

Ripped out my Injen short ram CAI and put the stock one back in. It's been 3 months, no idle problems or CELs.

[Liandri]

Originally Posted by shocksim

I had this same problem, at one point got a "Bank 1 Too Rich" CEL, went through a lot of troubleshooting. New colder spark plugs, cleaned air filter, cleaned maf filter, traced the intake for a vacuum leak, remounted the intake, and updated/reflashed a couple times.

Car would be fine til it started to settle into the tune and then would idle really rough every cold start and i would say every other cold start it would stall out. I'm only at 30K miles too.

Ripped out my Injen short ram CAI and put the stock one back in. It's been 3 months, no idle problems or CELs.

Nice. Yeah it seems to be common these cars don't take to changes in the intake well.

As an update to mine, it's been completely fine since unplugging the MAF for a few starts, plugging back in, clearing codes and resetting adaptations. Probably gone through 15 cold starts without a hiccup. Very weird