Engine stalling after some revs in Neutral

[JoepM5]

Hi guys,

Another question - I found out that my M5 stalled after revving it a bit in neutral. The car runs perfectly/smoothly otherwise (stable idle, pulling hard, no codes/warnings) but it keeps stalling if I rev it in neutral, both with a cold and a warm engine. I typically don't rev it in neutral but I'm pretty sure the car didn't stall when revving in neutral over the summer/autumn.

I searched for this topic/issue but couldn't find anything. I also have made a video of it, please see here (

). This was after a 20 mile drive (taking it easy, 2 hard pulls on the high way or so).

Does anyone know what can cause this?

Thanks a lot for any input!

Best,
Joep

[JoepM5]

Hi all,

Following up on the above post:
- I didn't drive the car much in the past 6 weeks but when I did it ran well (good cold start, steady idle, strong pulls)
-However, the issue on stalling/falling sharply in rpms after revving in neutral persisted so had it cheched out by a new (just relocated) local shop (BMW specialist, not necessarily M specialist) the other day
- They spent a few hours diagnosing the car with limited insights. The only things they did was extensive diagnosis (not really resulting in anything, except for a dynamic valve adjustment parameter being at 2000% where 200-300% was normal) and resetting the "adaption"/data (or something like it they mentioned). After this the car threw a "System too rich, bank 1" CEL. They told me to drive it for 130 miles/200km so the car could gather data again and return to the shop for further diagnosis.
- I have driven it 30 km since and the rpm falls have become more severe, it is dropping in rpms when pulling away at the traffic light (almost stalling) and also the rpms are less stable when idling

Please see another video below, I also turn on/off the AC at 19 secs and 31 secs which make the rpms drop for a bit.

https://www.youtube.com/watch?app=de...ature=youtu.be

I think I will bring the car back to the M specialist I have brought it before but in the meantime also searched the forum and seems like it can be anyone of 3 causes: leaking injectors / dirty MAFs / hpfp needing replacement.

Question: where would you guys start with new parts/work in this case?

Thanks a lot for any input!!

Best,
Joep

[M5_Raz]

Save your time with random shops and go to people that know this engine, not just M cars in general.

Hope you get it fixed soon!

[M5Rick]

First thing before anything clean tha MAF's with CRC spray.

[JoepM5]

Quick update - I cleaned the MAFs (very easy DIY) but this hasn’t really had any effect. Car starts and drives fine but especially when revving a bit in neutral it keeps stalling.

Any other suggestions on potential causes?

[M5Rick]

As a rule I don't rev the car in neutral.

[Blaxwil]

Stalling is a component of either air, fuel or a combination of both. I would first inspect all your vacuum hoses and air boxes for tight connections. Those quick revs at a standstill need both fuel and air ratios to be solid. If the ratios are off, there's a possibility of stalling out.

My guess is that you have a small vacuum leak that's just enough to cause a stall standing still but not enough to cause issues while driving.

[JoepM5]

Hi all,

As an update to this topic/issue:

Brought the car to an M specialist a few weeks ago to have this issue solved/sorted but despite a lot of effort still no solution:
- all injectors were replaced
- all spark plugs replaced
- Lambda sensors replaced
- cleaned the MAFs
- extensive vacuum leak testing without any results
- driving while monitoring all data/sensors
- compression / fuel pressure testing

Unfortunately all this hasn’t led to a solution or shown weird results. Seems like the HPFP is the last potential cause but what I find strange it that there is only an issue after idling / stop & go driving for a longer time with a warm engine (then the engine is running too rich and when revving in neutral or pulling away from the traffic light you notice it wants to stall). It revvs completely fine, and this is actually when it needs more fuel so I would say the HPFP should then be fine?

Does anyone still have any suggestions? To be honest I (and the M specialist) are a bit lost at this point.

Thanks a lot!

Best,
Joep

[M5Rick]

Air filters in good condition and no blockages or leaks from intake there presumably.,clamps are secure.

[JoepM5]

Originally Posted by M5Rick

Air filters in good condition and no blockages or leaks from intake there presumably.,clamps are secure.

Yes, that has all been checked. Could it be that the intercoolers are not letting through sufficient air?

[M5Rick]

Originally Posted by JoepM5

Yes, that has all been checked. Could it be that the intercoolers are not letting through sufficient air?

Unlikely and your M has highish mileage if I remember right. I'll take another shot in the dark and suggest a fuel additive to clean up coked up deposits in the engine.

[JoepM5]

Hi all,

Turner out to be on of the HPFP’s anyhow. Replaced both.

Happy to have it fixed!

Best,
Joep