[SlumpLord3000]

Just FIY I had my Cat but back in for inspection and the mechanic mentioned that my RPM would jump to 1000 and back down in a semi jittery way which happens instantaneously which I never noticed. Because it would happen within a second and be fine idling I thought it's just a car start. My idle is fine and I would never notice it. He said it happens with cat off and on but it's so minuscule that I never thought of it or noticed it so I don't bother with it. Maybe I have carbon build up and need walnut blasting but it doesn't affect my car in any meaningful way.

Once again I never noticed it until the shop said anything.

[Nick335iF30]

Also posted this on another post with same listed issues.

Here is that post.

I am pretty sure I have this issue solved. So a lot of people were saying that injectors solved it but that is a pricey endeavor for a rough idle.

I have a 2015 335 Sportline.
Mods:
VRSF high flow catted downpipe
BMS CAI
BMS Chargepipe


I decided to switch fuels to Shell VPowerNitro and then I did two cycles of running Techron fuel cleaner through it and it has not done it all week. I recommend not using local gas stations as the fill up with who ever is cheaper at the time. Doing this the car also responded better to throttle application. The cleaners must have cleaned up a gummed up injector or something.

I also did plugs and check charge pipes and stuff. Did nothing.

I also intend to tune the car with bootmod3 and hope it still remains fixed. I hope this helps!

[Stin999]

Was there ever any updates with the OP’s issue?

Had it been resolved?

Just started experience the exact same issue. Car (only on cold starts) will bog like it wants to stall, catch itself and spike the RPM’s, and then idle fine. Any off/on start the rest of the day is fine with zero issue. High paced driving is fine too no performance loss or any noticeable issue.

Only connection I’ve found is that flashing my car to stock or re-flashing my Bootmod3 map will make the issue stop for a couple weeks. Seems to come back though after awhile. Waiting for a response from PTF….

Help me get rid of this

[JaredG_F30]

I was having issues with this and it just got worse and worse, to the point where the engine would die. Then one day I'm cruising, hear a pop, engineer starts running really rough and I see a ton of white smoke coming from my exhaust. I pull over and stop the engine then have this overwhelming smell of unburnt fuel come over me. Iat that point I was pretty sure I just had an injector fail. Took it to my sho and yep, failed injector so I have them replace all my injectors. Got the car back and no more sold start issue.

;tldr: was having cold start issues and it turned out to be leaky injectors.

Originally Posted by Stin999

Was there ever any updates with the OP’s issue?

Had it been resolved?

Just started experience the exact same issue. Car (only on cold starts) will bog like it wants to stall, catch itself and spike the RPM’s, and then idle fine. Any off/on start the rest of the day is fine with zero issue. High paced driving is fine too no performance loss or any noticeable issue.

Only connection I’ve found is that flashing my car to stock or re-flashing my Bootmod3 map will make the issue stop for a couple weeks. Seems to come back though after awhile. Waiting for a response from PTF….

Help me get rid of this

[thejeremyman9]

There are reports of several people having good luck with running techron (usually a few treatments over 2-4 tanks of gas) to solve this type of problem. It's worth a try as a first test. If you run multiple treatments you might want to change your oil after.

Intakes are another common cause of cold start issues / idle issues, but don't really explain ones that get worse over time.

If reflashing your tune solves the problem, it could just be that doing so resets adaptations, so an adaptation reset might do the same thing. But if it comes back, its likely not a software issue.

[Doublen420]

Originally Posted by Blkjag09

Thank you!! I uploaded the video to YouTube..[IMG]

[/IMG]

I had the same issue, there was a vacuum leak in my chargepipe so during idle it would hesitate but under load there would no issues. Best option is to get a smoke test done to see where the leak it

[LA1Z24]

Direct Injected engine. Carbon build up on the back side of the intake valves.

[thejeremyman9]

Originally Posted by LA1Z24

Direct Injected engine. Carbon build up on the back side of the intake valves.

This usually isnt a problem with the N55. Several people have posted pictures of their valves before/after walnut blasting even at or above 100k miles and there is minimal buildup. Would only potentially be a problem if you had a deeper issue causing excessive oil in the CP system like excessive blowby.

But as the threads in this post allude to there are numerous issues that can cause rough idle.

[Stin999]

Originally Posted by thejeremyman9

There are reports of several people having good luck with running techron (usually a few treatments over 2-4 tanks of gas) to solve this type of problem. It's worth a try as a first test. If you run multiple treatments you might want to change your oil after.

Intakes are another common cause of cold start issues / idle issues, but don't really explain ones that get worse over time.

If reflashing your tune solves the problem, it could just be that doing so resets adaptations, so an adaptation reset might do the same thing. But if it comes back, its likely not a software issue.

Originally Posted by thejeremyman9

There are reports of several people having good luck with running techron (usually a few treatments over 2-4 tanks of gas) to solve this type of problem. It's worth a try as a first test. If you run multiple treatments you might want to change your oil after.

Intakes are another common cause of cold start issues / idle issues, but don't really explain ones that get worse over time.

If reflashing your tune solves the problem, it could just be that doing so resets adaptations, so an adaptation reset might do the same thing. But if it comes back, its likely not a software issue.

I can not figure it out man…

Another 2 weeks have gone by after switching from my old OTS Stage 2 map to new Flex Fuel Stage 2 map (per the request of Bootmod support).

Car ran perfect. Cold start bog went away and I thought it was fixed.

Just this morning it bogged again on it's initial cold start. Every other on and off after the initial cold start starts up fine with no issue. Absolutely no issues under full load or regular driving either, only that first cold start.

This is the 3rd time it's gone away and come back after about 2 weeks of flashing a different map.

I don't understand what would be causing the car to bog ONLY on the first cold start, would go away when flashing different maps and come back almost exactly 2 weeks later, and cause zero other issues with the car during heavy spirited driving, moderate driving, and on/offs the rest of the day.

[thejeremyman9]

Originally Posted by Stin999

I can not figure it out man…

Another 2 weeks have gone by after switching from my old OTS Stage 2 map to new Flex Fuel Stage 2 map (per the request of Bootmod support).

Car ran perfect. Cold start bog went away and I thought it was fixed.

Just this morning it bogged again on it's initial cold start. Every other on and off after the initial cold start starts up fine with no issue. Absolutely no issues under full load or regular driving either, only that first cold start.

This is the 3rd time it's gone away and come back after about 2 weeks of flashing a different map.

I don't understand what would be causing the car to bog ONLY on the first cold start, would go away when flashing different maps and come back almost exactly 2 weeks later, and cause zero other issues with the car during heavy spirited driving, moderate driving, and on/offs the rest of the day.

Now that it's happening again, does it happen every time (on the first cold start)?

The only thing i can think of with re-flashing fixing it temporarily is that i believe BM3 flashes reset all adaptations. I assume you rescanned for codes?

Cold start hiccups/issues are fairly common... if the car isnt stalling and its not causing other issues i would try not to lose too much sleep about it. Just keep an eye on it and make sure it doesnt get worse.

If it happens every cold start now you could try unplugging the MAF before starting the car and see if it still does it.

[Stin999]

Originally Posted by thejeremyman9

Now that it's happening again, does it happen every time (on the first cold start)?

The only thing i can think of with re-flashing fixing it temporarily is that i believe BM3 flashes reset all adaptations. I assume you rescanned for codes?

Cold start hiccups/issues are fairly common... if the car isnt stalling and its not causing other issues i would try not to lose too much sleep about it. Just keep an eye on it and make sure it doesnt get worse.

If it happens every cold start now you could try unplugging the MAF before starting the car and see if it still does it.

This morning was the first time it's done it since my last flash which was about 2 weeks ago. I'm assuming it will do it tomorrow now that it has done it once. It always follows the trend of once it does it one time it will keep doing it every other cold start. I can upload a YouTube video if you (or anyone) would like to take a look.

Maybe about a month ago I unplugged my MAF and sprayed it down with some cleaner when I was first trying to diagnose the issue. Did not help the issue.

Zero codes. I had a FMIC and turbo inlet installed about 2 weeks ago (during this issue) and they smoke tested the car. Found no leaks. My intake is the MPPK intake which has been on the car for about 2 years with zero issues. Filter changed about 3 months ago.

The shop hinted that maybe it's a HPFP or LPFP issue? I just don't understand how either could give me issues with only the cold start and not with any other driving though.

It's driving me nuts because:

A) it's embarrassing when someone else gets in with me on the cold start.

B) Right at the end of the bogging when the car catches itself, it revs the rpms up way higher than normal (I'm guessing to compensate) which makes it super loud and quite annoying. It then comes down and idles normal after.

[thejeremyman9]

Originally Posted by Stin999

This morning was the first time it's done it since my last flash which was about 2 weeks ago. I'm assuming it will do it tomorrow now that it has done it once. It always follows the trend of once it does it one time it will keep doing it every other cold start. I can upload a YouTube video if you (or anyone) would like to take a look.

Maybe about a month ago I unplugged my MAF and sprayed it down with some cleaner when I was first trying to diagnose the issue. Did not help the issue.

Zero codes. I had a FMIC and turbo inlet installed about 2 weeks ago (during this issue) and they smoke tested the car. Found no leaks. My intake is the MPPK intake which has been on the car for about 2 years with zero issues. Filter changed about 3 months ago.

The shop hinted that maybe it's a HPFP or LPFP issue? I just don't understand how either could give me issues with only the cold start and not with any other driving though.

It's driving me nuts because:

A) it's embarrassing when someone else gets in with me on the cold start.

B) Right at the end of the bogging when the car catches itself, it revs the rpms up way higher than normal (I'm guessing to compensate) which makes it super loud and quite annoying. It then comes down and idles normal after.

Did you actually start the car with the MAF unplugged though?

I find the fuel pump explanation unlikely. You could try logging fuel pressure on startup.

How old is your battery? Have you tried putting the car on a charger overnight and seeing if it still does it? IIRC one person had a old battery and voltage dropped too low on cold start and it caused a similar issue.

[Stin999]

Originally Posted by thejeremyman9

Did you actually start the car with the MAF unplugged though?

I find the fuel pump explanation unlikely. You could try logging fuel pressure on startup.

How old is your battery? Have you tried putting the car on a charger overnight and seeing if it still does it? IIRC one person had a old battery and voltage dropped too low on cold start and it caused a similar issue.

No I actually didn't. I just cleaned it, let it sit, plugged it back in, and started it up.

Are you suggesting on the next cold start I have it unplugged before I start the car? Start the car with it unplugged as well? What difference would that make? What information would that give me?

Logging a cold start is something I can do. I'll get around to it sometime this weekend and post the log in here.

Battery is almost exactly 1 year old. Had flashing issues last summer due to an old battery so I had it replaced at the dealer.

[thejeremyman9]

Originally Posted by Stin999

No I actually didn't. I just cleaned it, let it sit, plugged it back in, and started it up.

Are you suggesting on the next cold start I have it unplugged before I start the car? Start the car with it unplugged as well? What difference would that make? What information would that give me?

Logging a cold start is something I can do. I'll get around to it sometime this weekend and post the log in here.

Battery is almost exactly 1 year old. Had flashing issues last summer due to an old battery so I had it replaced at the dealer.

Yes, i am suggesting you unplug it and start the car with it unplugged. If the issue never occurs with the MAF unplugged it at least gives you a lead that the issue may be MAF related. Without the MAF plugged in the car will default to fuel tables instead of using the MAF to determine the amount of fuel needed.

[Stin999]

Originally Posted by thejeremyman9

Yes, i am suggesting you unplug it and start the car with it unplugged. If the issue never occurs with the MAF unplugged it at least gives you a lead that the issue may be MAF related. Without the MAF plugged in the car will default to fuel tables instead of using the MAF to determine the amount of fuel needed.

Interesting.

Well it looks like I've got a little experiment to do in morning.

I'll report back with the findings

[hardkandy]

Hi guys,

noob here with very noob question. My 2015 328i kinda jitter and rattle on cold start this morning (been parked for more than 24 hrs). Weather is slightly cold (10C). It last for about 10 secs before its stabilize and no rattle. When it rattles, it feels like the engine going to stall or something like that. Also there is this humming noise (not loud) from the engine bay and audible from the cabin. Thanks in advance.

[thejeremyman9]

Originally Posted by hardkandy

Hi guys,

noob here with very noob question. My 2015 328i kinda jitter and rattle on cold start this morning (been parked for more than 24 hrs). Weather is slightly cold (10C). It last for about 10 secs before its stabilize and no rattle. When it rattles, it feels like the engine going to stall or something like that. Also there is this humming noise (not loud) from the engine bay and audible from the cabin. Thanks in advance.

Post in your engine section, scan for codes, etc.

[n55david]

Originally Posted by hardkandy

Hi guys,

noob here with very noob question. My 2015 328i kinda jitter and rattle on cold start this morning (been parked for more than 24 hrs). Weather is slightly cold (10C). It last for about 10 secs before its stabilize and no rattle. When it rattles, it feels like the engine going to stall or something like that. Also there is this humming noise (not loud) from the engine bay and audible from the cabin. Thanks in advance.

you may want to ask the guys with a 328 man

[n55david]

Originally Posted by LA1Z24

Direct Injected engine. Carbon build up on the back side of the intake valves.

wrong forum man. this is the n55 group not the n54.

[VilleF30]

Originally Posted by thejeremyman9

Yes, i am suggesting you unplug it and start the car with it unplugged. If the issue never occurs with the MAF unplugged it at least gives you a lead that the issue may be MAF related. Without the MAF plugged in the car will default to fuel tables instead of using the MAF to determine the amount of fuel needed.

This ^. I had this cold start issue for a few months now trying to figure out what it was. I tried unplugging the MAF and starting the car letting the car idle for a few minutes and then replugging it once I turned it back off and the next morning it was gone and hasn't returned! For me not only did the cold start issue go away but the cars idle has been alot smoother and the shifts especially between 1-2 are noticably better.. After this worked I did some research and quickly changed my long overdue Engine Air Filter... Just in case there was a chance a clogged engine air filter could cause the MAF to get some weird vibes. Though the new filter should have definitely helped I must say that unplugging the MAF was the biggest difference.. It feels like a new car.

[LA1Z24]

OP are you on LI? Come to my shop so I can stick a borescope down the plug hole and confirm you need the intake valves blasted. I am still 95%+ confident this is your issue. It is a major issue on ALL gdi engines. Even when some people claim BMW is not affected...They certainly are.

[thejeremyman9]

Originally Posted by LA1Z24

OP are you on LI? Come to my shop so I can stick a borescope down the plug hole and confirm you need the intake valves blasted. I am still 95%+ confident this is your issue. It is a major issue on ALL gdi engines. Even when some people claim BMW is not affected...They certainly are.

Not diagreeing that DI engines don't fundamentally have more carbon buildup on the back of the valves as compared with port injection engines, but every single post ive seen on a F3x N55 before/after walnut blasting even at 100k+ miles shows that there is very minimal buildup and not enough to affect anything. If you have significant enough buidlup to cause a problem you would see oil in the TIC/IC/CP/etc, anywhere after where the CCV hose dumps into the inlet.