2008 BMW 135i Engine Misfiring/Sputtering - Diagnosis?

[BMWalb]

Hi guys,

I have a 2008 BMW 135i with about 40,000 miles on it. I have done some work to the car including: JB4 Tune, DCI, Cat-less downpipes, Charge pipe + BOV, FMIC, and Axle-back exhaust (about 5000 miles with the modifications).

I have not had any issues with the car and it has always been properly maintained.
In the past 2 months however, the car has shown some symptoms. In 2 instances, the car began to shake and stalled upon normal driving. However, I shut the car off and turned it back on and the issue went away. In the past week however, the car lost a tremendous amount of power and began to misfire - the check engine came on. I stopped at the closest auto shop (Autozone) and their diagnosis found that cylinder 4 was misfiring. Today I changed all of the spark plugs (Bosch OEM) to see if it would resolve the issue, but it did not. The car clearly still misfired and sputtered. I also switched coils 1 and 4 to see if was a coil issue and when I checked afterwards; instead of getting a misfire on cylinder 4, I got misfires on cylinder 1 and 3 and a (random cylinder misfire code). I would not think multiple coils just happened to fail today but I am not sure. I am aware that these cars are notorious for HPFP and Injector failures but I can not pinpoint what the issue is. I do not want to blindly purchase parts based on hoping it resolves the issue as these parts are not cheap. Any help or suggestions regarding similar experiences would be greatly appreciated.

I have posted a video showing the car at idle and misfiring/sputtering: https://youtu.be/P4usWAk6HFU

Thank you

[captainronno]

Did you find out anything? I had a similar problem with my 08 X5 (N52 motor) that I ended up fixing with just one new coil pack.

Misfire codes on 3 and 6, as well as a "Random/Multiple Misfire" code. I thought there was no way two coil packs would go out simultaneously, so I went right to swapping injectors around. That yielded no changes. I moved to the coils; swapped crappy 3 with 1, misfire and code disappeared. Swapped crappy 6 with 5, code jumped to 5. Replaced that one coil, no problems since. I have no idea why one bad coil would cause a misfire in a different cylinder, but that's what appears to have happened.

It's been a few hundred miles, and I'm holding my breath. I keep hearing cousin Eddie in my head: "She falls down a well, eyes go crossed, gets kicked by a mule, eyes go back...Iiii don't know."