[white.m235i]

I recently purchased a 15 M235i with some dinan goodies and every so often (happened 2 times since purchase about 2 weeks ago) I would start up the car and the cold start would hit around 1500 then it would dip to around 400-500 rpm for a second then come back to normal rpm (1100) then slowly go down to its normal running rpm. Anyone know what could be causing this? It doesn't happen EVERY start up but it is a little concerning. I've looked around a little bit and some people say that it could be the battery..? but I would like another opinion.

I will try to video record it happen but since it doesn't happen every time I cold start, it would be a little difficult.

[white.m235i]

Originally Posted by white.m235i

I recently purchased a 15 M235i with some dinan goodies and every so often (happened 2 times since purchase about 2 weeks ago) I would start up the car and the cold start would hit around 1500 then it would dip to around 400-500 rpm for a second then come back to normal rpm (1100) then slowly go down to its normal running rpm. Anyone know what could be causing this? It doesn't happen EVERY start up but it is a little concerning. I've looked around a little bit and some people say that it could be the battery..? but I would like another opinion.

I will try to video record it happen but since it doesn't happen every time I cold start, it would be a little difficult.

The dinan goodies I refer to are a dinan intake, dinan exhaust, and stage 2 tune (all installs were professionally installed). The previous owner had it done.

[3rdcoast228i]

How many miles on it?

And what kind of gas are you using?

[aozer]

Used to happen to mine on every cold start. It went away during the colder months of winter and hasn’t returned since. There are other threads on here and the 3/4 series forum about the same thing, nobody really knows what causes it.

[beMtroubleYou]

Originally Posted by white.m235i

I recently purchased a 15 M235i with some dinan goodies and every so often (happened 2 times since purchase about 2 weeks ago) I would start up the car and the cold start would hit around 1500 then it would dip to around 400-500 rpm for a second then come back to normal rpm (1100) then slowly go down to its normal running rpm. Anyone know what could be causing this? It doesn't happen EVERY start up but it is a little concerning. I've looked around a little bit and some people say that it could be the battery..? but I would like another opinion.

I will try to video record it happen but since it doesn't happen every time I cold start, it would be a little difficult.

Happend to me, twice but I had some faulty valvetronic servo and eccentric shaft.

Check codes. Valvetronic sensor faulty. Replaced, but then it happned once and havent since then. Happend when the car was warm. RPM didnt jump up as usually they do.

[white.m235i]

Originally Posted by 3rdcoast228i

How many miles on it?

And what kind of gas are you using?

almost 70k. 93 oct

[kivyee]

Any codes? Ghost or otherwise?

[Dylan86]

I have this on warmer ambient cold starts from time to time but it's just a slight drop. I have a feeling it's to do with my BMS intake, as I never had this happen with the OE intake. It did it really rough and almost stalled once or twice early in the spring time, but hasn't done that in over a month and was super cold outside when it did.. Strange.

I almost feel like the factory cold start is a bit too aggressive, to be honest, but it sure sounds cool

FWIW I'm also on fresh N20 spark plugs, and only run the ethanol free 94. This happened before and after the "tune up"

[bimmerfile]

Originally Posted by white.m235i

.................................................. ...................... I would start up the car and the cold start would hit around 1500 then it would dip to around 400-500 rpm for a second then come back to normal rpm (1100) then slowly go down to its normal running rpm. .................................................. ........

I've had this happen a few times over the past month - probably 1 out of every 5 starts. Never happened during cool or cold weather.
Seems not to be an uncommon occurrence with bimmers.
I don't think it has anything to do with your Dinan add-ons.

[kivyee]

I was just going to say it's potentially mod related, e.g. intake or air leak somewhere. Usually the rpm drop is due to something being outside of the parameters the DME is expecting, and adjustments have to be made to accommodate.

[beMtroubleYou]

Originally Posted by kivyee

I was just going to say it's potentially mod related, e.g. intake or air leak somewhere. Usually the rpm drop is due to something being outside of the parameters the DME is expecting, and adjustments have to be made to accommodate.

I dont think it is. I was stock when it happend! - it could be more noticeable with mods. Dunno!

[K8_M235i]

Dinan exhaust doesn't have a valve. Could it be less back pressure on cold start causing rpms to drop?

My fiend that had a m235i had the valve unplugged and sometimes his would stall on cold start. When the car is running the secondary air pump on the cold start it probably expects more back pressure.

Just a theory.

[beMtroubleYou]

Originally Posted by K8_M235i

Dinan exhaust doesn't have a valve. Could it be less back pressure on cold start causing rpms to drop?

My fiend that had a m235i had the valve unplugged and sometimes his would stall on cold start. When the car is running the secondary air pump on the cold start it probably expects more back pressure.

Just a theory.

No, its something else. As I said I was bone stock, but then again I had a faulty ecentric shaft and those do affect start/stop sequence and idle among other things.

[bmays909]

Originally Posted by beMtroubleYou

No, its something else. As I said I was bone stock, but then again I had a faulty ecentric shaft and those do affect start/stop sequence and idle among other things.

Did you ever figure out what the issue was? My M235i is having the same problem on cold start.

[KennyFSU]

Mine did that with a BMS intake, replaced it with a K&N panel filter and the car has been running better ever since.

[Liandri]

I had this consistently happening on my 2016 with low miles and was not modded at the time. I logged fuel pressure high and low side, nothing abnormal. No codes, no other indicators of the phenomenon on the scan tool, it was like the DME didn't know it was happening at all, which is super odd for such an extreme event that happens every day. Coils and plugs did nothing to fix. Resetting the DME adaptations would fix it for a week or two then it would return. After browsing all the threads repeatedly until my brain couldn't handle it anymore, I chalked it up to a bug in software. I flashed mhd and disabled cold start and it hasn't happened in 5 months of daily driving. Lots of people have similar stories, and there seems to be no proven cause or fix. For me it happened on the original 2016 firmware as well as the latest 2019 firmware when I had the cars firmware updated before starting to mod

[beMtroubleYou]

Originally Posted by bmays909

Did you ever figure out what the issue was? My M235i is having the same problem on cold start.

If its only during cold starts then its something else.

Maybe a leak? Mine was, like I said eccentric shaft gone bad due to faulty valvetronic motor.