[john_s]

Hi folks, I got a misfire that's super difficult to diagnose. It's a 2008 e92 m3, completely stock, daily driver, 130k miles. A month ago when I drove back from work, when I came to a red light, it suddenly went into limp mode. I was 2 minutes away from home, so I drove it slowly to home. Note that this is exactly one day after the dealer did the positive battery cable recall.

Here is the symptom: immediately (~2 second) after the car starts, it went into limp mode, and throws cylinder 1,2,3 misfire code, and the general "multiple misfire" code. No other code ever. Just pure misfire of almost one bank. It throws these code 100% of the time, consistently immediately after the start. Both exhaust have unburnt fuel, I can see thin white smoke and smell the heavy fuel smell. If I went under the car after it limps for 1 minute, only driver side exhaust is hot. The passenger side (bank 1) exhaust is completely cold.

I have done days of research and have now replaced ALL 4 O2 sensors (2 pre cat 2 post cat), Both exhaust gaskets, fuel tank breather valve, spark plugs, and fuel injectors. The coil packs are not the problem, I swapped them around the misfire didn't follow, and I did a spark plug test with those coils and I can see sparks firing correctly. ISTA+ also confirms all spark plugs firing intervals are fine. In ISTA+ I can see cylinders 1,2,3,4 are completely dead, have 0 combustion. When I start the engine, cylinders 1,2,3,4 have combustion, but then very quickly died. I have also confirmed both the old and new fuel injectors are working by pulling them out and squirt on towels.

I'm starting to lose my sanity now. I'm thinking idle control valve, but the ICV feeds air to both banks simultaneously, why only bank 1 misfires? I remember reading somewhere that if the ICV fails, the throttle actuator takes over at idle, the engine doesn't misfire, it just idles higher. Throttle actuator has been replaced and is working fine.

Or did the dealer screwed up something electrical? If that's the case I should get the error immediately at the dealer lot, but not one day after 50 miles of commute.

Is there anything else on the S65 engine that is one-bank only? Vanos? Timing related?

Any help appreciated, thanks!