[Jaszm]

2015 535i. Sometimes on a cold start the RPM will quickly drop and quickly go up (up to about 2k) for a second and go back down to normal. No codes/CEL.

I thought this might have to do with a cold climate, but today it was around 46 degrees F.

Does anyone else have this issue?

[S1nner]

Never happened on a cold start. Usually happens after a quick drive on the next start.

[ednyc2nc]

I my car does it 2 every morning but no check engine lights yet.

[bake]

It might be your valvetronic motor. Mine was doing the same thing for a long time then progressively got worse. When I had an indy shop check there were stored codes for a valvetronic motor code. A trip to the stealership confirmed the same. It was a $2,200 job at the stealership, but it comes with a 2 year warranty on the work.

[OnlyGerman]

I have learned these cars do weird things when cold

[mfractal]

happens rarely on cold starts here too.. it's fine.

[BurrNinja]

Same here not all the time either. Ive tried tripping a cel or something by putting in drive during the blip of rpm it stumbles but catches itself and smooths out. I will be getting a laptop soon and gonna scan my car with the software.

[obiltagi3]

Spark plugs?

[Bmwdoubles_]

Make sure you have no unmetered leaks. Anything after the MAF that is not secure can cause that too. Smoke and pressure test will reveal it. Also reset adaptive intake mass flow if you have mhd

[ProjektAutoScott]

I've been through about 30 N55 powered bimmers in the last four years (dealership). I've daily driven plenty of them cold and hot. Half of them do it, new or old. Seems to happen more with the X5s and X6s, then 535s, and rarely 335/435s. Regardless, these engines have a mechanical fuel pump and a lift pump. It seems they lose prime occasionally if started before the lift pump can catch up. Metering freaks out, and it over-compensates with throttle or extra fuel for whatever reason. It might be a software thing too. I've noticed it happens less if you turn the IGN on and wait until the lift pump stops buzzing before starting.

Either way, your fine. When I first noticed it I would scan every car for DME codes constantly to no avail. The local dealer here agrees it's normal too for n55 cars. No need to stress or panic about it... If you have codes for something, they are likely unrelated and of course, should be addressed. However, you can go insane trying to nail down an issue; don't replace a bunch of parts because someone on the internet scared you. Your car is smart enough to know if you have a boost/vacuum leak, bad plugs, coils, injectors, fuel pressure issues etc.. It would eventually throw misfire codes and mixture faults if this were the case.

[Jaszm]

Originally Posted by ProjektAutoScott

I've been through about 30 N55 powered bimmers in the last four years (dealership). I've daily driven plenty of them cold and hot. Half of them do it, new or old. Seems to happen more with the X5s and X6s, then 535s, and rarely 335/435s. Regardless, these engines have a mechanical fuel pump and a lift pump. It seems they lose prime occasionally if started before the lift pump can catch up. Metering freaks out, and it over-compensates with throttle or extra fuel for whatever reason. It might be a software thing too. I've noticed it happens less if you turn the IGN on and wait until the lift pump stops buzzing before starting.

Either way, your fine. When I first noticed it I would scan every car for DME codes constantly to no avail. The local dealer here agrees it's normal too for n55 cars. No need to stress or panic about it... If you have codes for something, they are likely unrelated and of course, should be addressed. However, you can go insane trying to nail down an issue; don't replace a bunch of parts because someone on the internet scared you. Your car is smart enough to know if you have a boost/vacuum leak, bad plugs, coils, injectors, fuel pressure issues etc.. It would eventually throw misfire codes and mixture faults if this were the case.

I actually had a video about it and posted it on a FB group where I was told it was the HPFP, but I was a bit skeptical about it bc of no codes. And the car runs smooth otherwise.

This definitely gives me more peace of mind, thanks for the info!