BM3: Sudden cold start stall issue solved by re-flash?

[calubi]

All of a sudden my M3 developed a cold start idle issue today. I've been running the BM3 stage 1 93 octane tune for a few weeks now, along with a BMS intake. Never had the car stall before, but today it would seemingly idle fine for 5-6 seconds, and then cut out. No apparent roughness or stumbling, the car literally felt like I hit the ignition button to turn it off. Tried several times, all the same result. Even using the throttle to try to keep the RPMs up did not help; just stopped running after 5-6 seconds.

After a quick visual check under the hood (nothing suspicious), a code scan (no codes in BM3 app), and a reset of adaptations (again, still won't idle for more than 5-6 seconds afterwards), I decided to try a re-flash of the same tune file. After the flash, it started right up and kept going. Smooth idle (cold start delete), drives fine.

Anyone seen this before?

I've been trying to think of anything mechanical that would be different between pre-flash and post-flash:

- The engine would have been slightly warmer from the previous idle cycle
- I turned off the HVAC to flash, so HVAC was ON before the flash and OFF after the flash.

These seem unlikely: the change in temperature would be small, and I've never had an idle problem with HVAC before. If there was something wrong, I would expect the car to struggle to idle a bit before stalling, not just kill the engine.

[4everkidd]

The cold air intakes have been notorious for rough cold starts in cold environments.

The fact that it fired right back up after the reflash is most likely due to the warmer environment.

I personally believe it has something to do with the metal MAF sensor mounts in cold weather although I have no substantiating evidence. I do however have to remove my intake every winter.

What was the delta in outdoor temps?

[calubi]

The car was garaged and ambient temperature was maybe 35 degrees?

The part I find weird is that the car never showed signs of stumbling or typical rough idle like wandering or erratic RPM. It would always fire right back up and feel fine, just turn off after a few seconds. Is that normal for cold weather intake issues?

[calubi]

I finally got around to swapping back to the stock intake (minus the charcoal filters). I also updated to the latest v9.1 OTS map. Ran fine the first day immediately after the reflash. But today I had some roughness when I tried to reverse out of the garage. Idle seemed fine, but it choked and stalled when I tapped the throttle in reverse. So swapping back to the stock intake just changed the symptoms a bit. Without any throttle input, idle seemed stable. Ambient temps were around 45. A couple of hours later I was able to start it up and pull it into the garage just fine, but I did turn the HVAC off first.

Next on the list of things to try:

1. Reflash with stock tune to see if this resolves the issue, pointing to the tune being the issue.
2. Make sure HVAC is turned off. This is a factor I've seen mentioned on here, and it's usually inconsistent in my testing. It's OFF right after a flash since I make sure it's off before flashing, but it's ON for later starts. Thoughts?

Assuming the stock tune resolves the issue:

1. Try stage 1 tune again with cold start ENABLED. Maybe the higher idle RPM is needed for the engine to run properly and heat up the first few minutes in colder weather. Thoughts?
2. Try another OTS map, like CS or GTS.

If the stock tune exhibits the same issue, then the next thing to try would be pulling the plugs and widening the gap. At the same time as I put the intake on, I swapped to NGK plugs with a 0.022" gap, per the BM3 wiki. Could this be an issue in colder weather? If so, I would have expected a rough idle overall, not just when starting from stop.

Anything else to add to the list of things to try?

[Tommy L Garage]

Is your cold start deleted? If so that’s the reason.

[calubi]

Yes, cold start is deleted. Mostly to not be obnoxious on start up. Can you elaborate on what causes such an issue with cold start delete? Before deleting it, I read several threads on here and they all suggested that it just helps to heat the cats, but does not otherwise affect anything drivability-related. I'm not doubting, I'll definitely try this as its an easy toggle. Just curious...

[MR RIZK]

As Tommy L Garage mentioned enable the cold start. I remember quite a few threads a while back about this. I don't think a root cause was ever found.

[ntg44]

Originally Posted by calubi

Yes, cold start is deleted. Mostly to not be obnoxious on start up. Can you elaborate on what causes such an issue with cold start delete? Before deleting it, I read several threads on here and they all suggested that it just helps to heat the cats, but does not otherwise affect anything drivability-related. I'm not doubting, I'll definitely try this as its an easy toggle. Just curious...

Have you ever tried starting a carbureted engine in the cold without the choke pulled? Same concept, even though modern cars are EFI. Engine needs to warm up. Sure, there are probably no issues with cold start delete in warmer climates, but when you get to near freezing temps, fluids are thicker and it requires a higher idle. The intakes make it even worse because the idle is even jumpier. The colder the engine, the higher the idle needed to keep it from dying.

Nothing new here.

[calubi]

Just to update, the car has been doing fine in even colder weather with cold start at OEM settings. No starting issues in the last couple of weeks since changing it. Thanks everyone!

[danniexi]

Originally Posted by calubi

Just to update, the car has been doing fine in even colder weather with cold start at OEM settings. No starting issues in the last couple of weeks since changing it. Thanks everyone!

yes, it’s loud and annoying as hell, but cold start (OEM settings) helped sold those issues for me as well.