[Dave92N54]

I've experienced this honestly I think since purchasing the car, and it's been such a rare occurrence I've never been able to log it and never really worried about it. I felt it coming today, I can't describe it other than that, so I hit log and sure enough I finally caught it.

This time it happened after a warm start but sometimes it will just happen when sitting at an idle for a bit, or pulling up to a stop. Essentially my RPMs will jump up like 100 and come right back down, and that's it. Only does it once. Curious to find out of this is normal, or if any of you have experienced it.

https://datazap.me/u/e92dave/small-j...6-85-103-75-76

It seems to be WGDC related, if you look the WGDC shoots from ~44 to ~51 exactly when it happens. Throttle stays steady. I assume this is likely because the wastegates closed a little more and the car just had to adjust the idle but, is this normal? This log was started probably 30-45s after a warm start (the car had been sitting for roughly an hour after driving, oil temp had reached about 220-230). I appreciate any responses.

[Bimmer_Bro]

Originally Posted by Dave92N54

I've experienced this honestly I think since purchasing the car, and it's been such a rare occurrence I've never been able to log it and never really worried about it. I felt it coming today, I can't describe it other than that, so I hit log and sure enough I finally caught it.

This time it happened after a warm start but sometimes it will just happen when sitting at an idle for a bit, or pulling up to a stop. Essentially my RPMs will jump up like 100 and come right back down, and that's it. Only does it once. Curious to find out of this is normal, or if any of you have experienced it.

https://datazap.me/u/e92dave/small-j...6-85-103-75-76

It seems to be WGDC related, if you look the WGDC shoots from ~44 to ~51 exactly when it happens. Throttle stays steady. I assume this is likely because the wastegates closed a little more and the car just had to adjust the idle but, is this normal? This log was started probably 30-45s after a warm start (the car had been sitting for roughly an hour after driving, oil temp had reached about 220-230). I appreciate any responses.

Mine has done this since day 1 during idle. It has never caused any problems or concerns for me. Never logged it either. I just assumed it was something turning on or off. (Like a pump or something).

[Dave92N54]

Originally Posted by Bimmer_Bro

Mine has done this since day 1 during idle. It has never caused any problems or concerns for me. Never logged it either. I just assumed it was something turning on or off. (Like a pump or something).

Was my assumption but since I managed to log it, figured i'd see if it really was normal. I appreciate the response, thank you!

Also, anyone else's BimmerPost app finally start working properly? I've been using the app for months and never got a push notification, starting yesterday I seem to get them now

[Bimmer_Bro]

Originally Posted by Dave92N54

Was my assumption but since I managed to log it, figured i'd see if it really was normal. I appreciate the response, thank you!

No problem! Maybe it has something to do with vacuum pump or pressure since you are seeing the waste gates react at the time same .

[Dave92N54]

Originally Posted by Bimmer_Bro

No problem! Maybe it has something to do with vacuum pump or pressure since you are seeing the waste gates react at the time same .

Just had that thought as well, definitely could be along those lines. Oh well, I won't think twice about it anymore.

[Saif2018]

Originally Posted by Dave92N54

I've experienced this honestly I think since purchasing the car, and it's been such a rare occurrence I've never been able to log it and never really worried about it. I felt it coming today, I can't describe it other than that, so I hit log and sure enough I finally caught it.

This time it happened after a warm start but sometimes it will just happen when sitting at an idle for a bit, or pulling up to a stop. Essentially my RPMs will jump up like 100 and come right back down, and that's it. Only does it once. Curious to find out of this is normal, or if any of you have experienced it.

https://datazap.me/u/e92dave/small-j...6-85-103-75-76

It seems to be WGDC related, if you look the WGDC shoots from ~44 to ~51 exactly when it happens. Throttle stays steady. I assume this is likely because the wastegates closed a little more and the car just had to adjust the idle but, is this normal? This log was started probably 30-45s after a warm start (the car had been sitting for roughly an hour after driving, oil temp had reached about 220-230). I appreciate any responses.

Wouldn't worry about that mate. My car has the idle set to 750rpm, after the cold start, it would drop to about 650rpm, then in a split second back to 750rpm and remain there.

We get really sensitive every little thing since we had these cars for a while lol.

[Dave92N54]

Originally Posted by Saif2018

Wouldn't worry about that mate. My car has the idle set to 750rpm, after the cold start, it would drop to about 650rpm, then in a split second back to 750epm and remain there.

We get really sensitive every little thing since we had these cars for a while lol.

Yeah I have mine set to 700. Wasn't really worried as much as I was curious, either way, I try my hardest to stay proactive about any issues before they wreak havoc so figured i'd ask since I got a log. I appreciate the response though, thank you!

[Saif2018]

Originally Posted by Dave92N54

Yeah I have mine set to 700. Wasn't really worried as much as I was curious, either way, I try my hardest to stay proactive about any issues before they wreak havoc so figured i'd ask since I got a log. I appreciate the response though, thank you!

can't argue about being proactive.

[Dave92N54]

Reviving this because it seems like it's getting worse.

Had to take a trip to the MVA today (for those in the U.S. that don't live in Maryland, that's the DMV), it went surprisingly well. Drove my way back, hopping on it a few times, even gave a very clean S4 a fender

I go to park the car, and it's doing what i've described here, so I let it idle for a bit. All of a sudden the AFR drops on both banks simultaneously, trims on both banks went to about -10% and then AFR went to probably 16, trims to -4%, and it kept doing this for a bit until it smoothed out. Stupidly I didn't log it... I just sat there and watched my gauges like an idiot. I did however notice my boost gauge fluctuate a bit while it did this, not much but a bit. I'm usually around -9 to -10 at idle, and when this was happening it was showing like -9.4, -9.6, -9.8, -9.6, -9.8, -9.4 and was bouncing around those values. Almost makes me think there's a leak somewhere after the throttle? Or maybe MAP sensor is bad, but why no code?

Does anyone have an idea just off the top of their head? I have class in a bit and i'll take it for some logs after to see if anything looks amiss. It felt normal when I had been driving it.

Edit: Forgot to mention, when I started it up to leave initially I got a puff of blue smoke out the back. I am aware of my turbos failing, if any of you have seen my turbo thread you know I'm waiting on a set of RB billets. Wondering if that's having any affect, oil affecting afrs maybe? I don't believe the smoke is valve stems (I'm sure that will be a conclusion made because it happened after startup) the previous drive I had made was fairly vacuum heavy, wouldn't be surprised if there was oil just sitting in the turbo when I started it.

[Zach1328]

Don't take this as a perfect science since it's one example. However, when I blew one of my stock turbos the car dumped ~5-6L of oil into the exhaust. Some of it is still burning off about a year and 2,000+ miles later. I did replace the two pre-cat O2's after the failure but the post-cat were nearly brand new so I left them.

Even with 5L+ of oil dumped into the exhaust I never had any issues. I don't think a little oil from failing turbos should be much of an issue. Whether or not there's some sort of leak, waste-gate, or whatever other problems would just be a guessing game without more hard data.

If you're actively waiting on RB's then let those come in. Check the basics during install. If nothing is obviously out of place then install as usual and wait to see if these symptoms/problems still occur.

Doesn't sound like anything is in serious danger if you're logs look good at WOT, so I wouldn't be too concerned. Some hiccups and lean AFR's at idle won't hurt anything. Different story if you're having those issues at high RPM's and 20psi or something like that.

[NoGuru]

I bet your O2's are getting messed up a little from the turbos going. Might want to replace them when you do the turbos.

[Dave92N54]

Originally Posted by NoGuru

I bet your O2's are getting messed up a little from the turbos going. Might want to replace them when you do the turbos.

Well, I hooked up INPA and watched 02 voltages at idle for a few minutes, no problems.

I am definitely considering turbos to be the issue. Wastegates acting weird causing unexpected air, oil seeping past. It's not a major issue, no codes either so i'm going to just ignore it until they're replaced. If it continues i'll start digging.