Rough Idle at Startup

[///Mvy]

I have a 2015 M3 with a few mods but recently it's been running really rough at startup and even stalled a few times. It's only after starting, in the first minute or so. Warm or cold. RPMs studder and will fall to 500rpms then bounce up to 1200rpms when it tries to catch itself. Almost sounds like a lopey idle.

Once I put it in gear and start moving, feels great. No hiccups and I can still spin through first and second gear.

I've put 200 miles on it since this started... hoping it would pop a code but I'm not seeing any.

2015 M3 DCT 44k
-BM3 S1 with coldstart delete
-VRSF Single mid (just installed but there aren't any sensors or anything that I could've missed plugging back in)
-Intakes
-Fresh plugs, properly gapped, 1,500mi ago

So far I've checked codes, reset adaptations, checked MAFs and Intake vacuum lines. I'll check LTFT and I'll probably turn cold start delete back off and see how it runs but it's so loud! Any other ideas to check?

[MJ6]

Originally Posted by ///Mvy

I have a 2015 M3 with a few mods but recently it's been running really rough at startup and even stalled a few times. It's only after starting, in the first minute or so. Warm or cold. RPMs studder and will fall to 500rpms then bounce up to 1200rpms when it tries to catch itself. Almost sounds like a lopey idle.

For an issue like that I might check your primary oxygen sensors. Since they essentially act as your DME's eyes and tell it what the engine is doing, a failing o2 sensor could potentially cause idle issues.

[TopJimmy]

I had that happen from a cracked ceramic on a plug. The crack was behind the ground strap and hard to see until after I pulled it and inspected under bright light. My idle was crap, but revving cleared it up. I had to find the problem, and that's what it was.

[///Mvy]

Originally Posted by MJ6

For an issue like that I might check your primary oxygen sensors. Since they essentially act as your DME's eyes and tell it what the engine is doing, a failing o2 sensor could potentially cause idle issues.

Anything I could log to check for it failing?

Originally Posted by TopJimmy

I had that happen from a cracked ceramic on a plug. The crack was behind the ground strap and hard to see until after I pulled it and inspected under bright light. My idle was crap, but revving cleared it up. I had to find the problem, and that's what it was.

Interesting... did you have a misfire code or anything to hint you towards that?

[theweebabySeamus]

Can't intakes cause this? Or is it more subtle?

[MakeMuricaGreater]

I had the same exact issue. Car would start, then sound like it hiccuped and go completely silent, then RPM's would jump before stabilizing somewhat.

I ignored it until I subsequently started catching misfires in the high RPM range whilst highway driving.

Sure enough, cylinder two had a misfire. Replaced all of my spark plugs with the recommended NGK's at 0.022 gapping and fresh Delphi coils. Car runs like a dream now.

Edit: FWIW, I've seen other members describe issues with certain OTS tunes causing weird idle problems. It appears the general consensus was swapping to a different tune, then reverting back or a mix of this.

[TopJimmy]

I had no codes. Just rough on idle, enough to shake the TMIC.

[jpy1980]

Hands down it’s the intakes combined with the cold start delete. I know this because I had the same issue.

If you don’t want to uninstall the intakes, then just put COld start back on.

[4everkidd]

It's the intakes. Cold start or not.

What brand? I'm assuming aluminum.

Do a search on it; those of us with this issue in colder climates it will quite literally stall the car

[Kilabyte]

Originally Posted by jpy1980

Hands down it’s the intakes combined with the cold start delete. I know this because I had the same issue.

If you don’t want to uninstall the intakes, then just put COld start back on.

Nah, just gap your plugs right, worked for me

Intakes and cold start delete and the only time it feels like stalling is if I try to drive off in the first 30 seconds or so without blipping the throttle

[Cboy]

Originally Posted by ///Mvy

I have a 2015 M3 with a few mods but recently it's been running really rough at startup and even stalled a few times. It's only after starting, in the first minute or so. Warm or cold. RPMs studder and will fall to 500rpms then bounce up to 1200rpms when it tries to catch itself. Almost sounds like a lopey idle.

Once I put it in gear and start moving, feels great. No hiccups and I can still spin through first and second gear.

I've put 200 miles on it since this started... hoping it would pop a code but I'm not seeing any.

2015 M3 DCT 44k
-BM3 S1 with coldstart delete
-VRSF Single mid (just installed but there aren't any sensors or anything that I could've missed plugging back in)
-Intakes
-Fresh plugs, properly gapped, 1,500mi ago

So far I've checked codes, reset adaptations, checked MAFs and Intake vacuum lines. I'll check LTFT and I'll probably turn cold start delete back off and see how it runs but it's so loud! Any other ideas to check?

It's your intakes + cold start delete.

If I drive off too fast even with cold start the car stumbles. If I wait 30 seconds before moving it's fine.

[jpy1980]

Originally Posted by Kilabyte

Nah, just gap your plugs right, worked for me

Intakes and cold start delete and the only time it feels like stalling is if I try to drive off in the first 30 seconds or so without blipping the throttle

Hmm are you tuned? What gap did you go with? I went with a .023 gap and I'm on Stage 1. I gapped them prior to actually going to BM3 Stage 1. I wonder if I should've gone smaller

[Kilabyte]

Originally Posted by jpy1980

Hmm are you tuned? What gap did you go with? I went with a .023 gap and I'm on Stage 1. I gapped them prior to actually going to BM3 Stage 1. I wonder if I should've gone smaller

I am, stage 1, NGKs gapped to .20

[NYG]

I know you did some changes to the car which could have impacted how much/how little the rough idle at cold start is but if it's any consolation every DI engine that I've ever had, stock, had rough idle until exhaust sensors got hot enough to operate.

[TopJimmy]

Originally Posted by jpy1980

Hmm are you tuned? What gap did you go with? I went with a .023 gap and I'm on Stage 1. I gapped them prior to actually going to BM3 Stage 1. I wonder if I should've gone smaller

0.023" is right for Stage 1 and 2...all flavors. (Recommended by PTF)
0.021" is for Custom E85 tunes. (rec'd by F80P)
Down to 0.018" only as needed to counteract spark blowouts on very high boost cars, but not unless needed (as per F80P).

I was doing a F80P E85 race tune so I gapped NGKs to 18 got a terrible bad idle...opened them back up to 21 and I was good again. Still 21 gap and 28PSI running at the 1/4mi drag strip no probs.

[///Mvy]

Originally Posted by 4everkidd

It's the intakes. Cold start or not.

What brand? I'm assuming aluminum.

Do a search on it; those of us with this issue in colder climates it will quite literally stall the car

Burger Motor Sport.

Thanks everybody for the info. Did some searches and it seems like the intakes add up to the issue. Interesting that this wasn't an issue until I put the mid pipes on. Maybe the extra flow was enough to mess up the dme.

Anyways, not too worried about it. I turned cold start back on and I haven't felt any hesitations.

[Kilabyte]

Originally Posted by ///Mvy

Burger Motor Sport.

Thanks everybody for the info. Did some searches and it seems like the intakes add up to the issue. Interesting that this wasn't an issue until I put the mid pipes on. Maybe the extra flow was enough to mess up the dme.

Anyways, not too worried about it. I turned cold start back on and I haven't felt any hesitations.

I have the same intakes.

[Graves]

I know this is an old post, but I am still having this issue. It’s been ongoing for a couple years now. I have Eventuri intakes (the full system utilizing the scoops behind the kidney grills). I just replaced the plugs and gapped them at .021 per Paul Johnson and my tune. Fresh Delphi coils. Bank 1 & 2 codes are on. I replaced bank 1 but couldn’t get to bank 2 due to the downpipes so I will have to take it somewhere for that. Anyone had issues with thier Eventuri’s? I am thinking two things:

1. Bank 2 just needs to be replaced, clear codes, reset adaptations and boom, maybe that solves the final piece of the puzzle.

2. Take the scoop portion of the Eventuri system off and just run open filters. Maybe it struggles to pull air due to the length it needs to travel. I don’t think this is the issue though, but you never know.

Car idles and runs perfect once it settles and during driving. Pulls good and hard.

[MetzgerMeister]

I solved this issue by replacing the turbo inlet O-Rings.

DIY here:

https://f80.bimmerpost.com/forums/sh....php?t=2108699

It also solved an issue I was having whereby the engine would stutter when going up an incline - engine would rev but half stalled until the car realised it had to drop down a gear.

[vlad28]

Have the same issue of rough idle on startup, the car has only BM3 stage 1 and a new spark plugs from the previous owner. Does one of those could cause that issue?

[vlad28]

And does anybody know what is the perfect spark plugs gap for BM3 stage 1?

[Graves]

Welp, did the following 2 weeks ago and still had a rough idle:

New plugs
New coils
Clean MAF sensors
Replaced Bank 1 o2 sensor

Fast forward to today:

had BMW replace the Bank 2 o2 and the rough idle is gone. Zero issues now (knock on wood). I figured it was the o2, just glad that was all it was.