Cold Idle Misfire Problem, help wanted please...

[M5Rick]

Might also be worth checking the efficiency and security of the aftermarket air filters/trunking as a whole you have in place,oiled filters are no-no in these.
GL.

[325_bucks]

Originally Posted by M5theonlyone

Might also be worth checking the efficiency and security of the aftermarket air filters/trunking as a whole you have in place,oiled filters are no-no in these.
GL.

Yeah fair point, it's a non oiled Eventuri intake so should be pretty good, but I could always replace it with oem intakes just to see, but I am quite confident it's not the intake that's the issue here....well fairly confident anyway!

[Rjrzwhips]

Check the voltage of your battery. My symptoms were similar to yours. I would start the engine and it would run normal for a few seconds then the idle would start to surge. I disconnected the battery and charged it which took a few hours. The idle was normal after the charge.

[325_bucks]

Originally Posted by Rjrzwhips

Check the voltage of your battery. My symptoms were similar to yours. I would start the engine and it would run normal for a few seconds then the idle would start to surge. I disconnected the battery and charged it which took a few hours. The idle was normal after the charge.

Did you check the voltage with a meter across the terminals? What should it be ideally?

[325_bucks]

Currently getting 11.9v across the battery, how does that sound?

[Rjrzwhips]

That is a bit low. Normal I believe should be between 12.2-12.6. Have the battery charged and see if it solves your problem

[Spacecpe]

Mmmmm very strange.. I thought it would be O2 related for sure. Ive seen batteries cause some very weird issues before, its a possibility.
Would be very nice if the incident could be logged so we can have something to work with.
You said you have new MAFs right? Take a look at the map sensors and give them a clean.. I had a very weird cold start issue before on my N54 where the car would start fine then the AFRs go full lean. Turned out to be the TMAP sensor that was on the intake manifold.. almost sounds familiar to your issue..

[325_bucks]

Update on this, I took the plunge given the old battery was original and I hear these cars can eat batteries.

So new battery installed. Interesting, first start after new battery, the idle was different to how it was before, after the first 30 seconds, it wasn’t 100% not moving at all, there was certainly a little fluctuation but nothing like it was before. I wonder if it could be as simple as this or whether this was a false result. If it is battery related then there could be a battery drain somewhere.

Battery voltage before starting (new battery) was 12.2v and after a short drive was also 12.2v

I need to see how it is tomorrow. That’s the real test I guess.

[rickyf10]

Mine once had similar problem, it turned out to be a faulty fuel pump

[Spacecpe]

That sounds great. Keep monitoring and update us.
Bmws are very finicky with low voltage.. had a few encounters with them.

[325_bucks]

Originally Posted by E90 M335i

That sounds great. Keep monitoring and update us.
Bmws are very finicky with low voltage.. had a few encounters with them.

Update from today, first start today was pretty much like yesterday with the new battery. Different from before but not gone, still idles weird. Yesterday the battery was new off the shelf when I started it and after starting I only took it for a short drive so it’s possible I didn’t condition the battery correctly after installing but today I took it for a long drive so we’ll see tomorrow what happens I guess. Oh and while I’m writing this I just realised I need to register the new battery too because it won’t be charging right until I do.

If not the battery, I guess I’m left with injectors, fuel pumps/filter, anything else? I assume the injectors are a huge job to change!

[aleks_m5]

I have the same issue on my 2015 M5. I also run bootmod3 and have searched for a solution. I turned off the Cold Start as well and have noticed an increase in fluctuations. Someone told me to clean the MAF and I did try that but it only helped for maybe a few hundred miles then went right back to normal. Very interested to see what people come up with!

[Kprad12]

My car has this issue too. Not tuned but recently installed downpipes and intakes as well as changing all sparkplugs. Really am a bit paraniod that its injectors as that can result in engine failure. if anyone gets it fixed let me know. Dam BMW injector warranty that only replaces injectors after your engine fails