Last night, car started to idle pretty rough and would sometimes stall when in neutral. Turned the car off and it would start for a brief second and then die again. Used BT Tool and scanned to see any codes and it came back with:

2D9B Knock Sensor, Signal
2B56 Mass Air, Plausibility

I took apart the filter box and inspected the air sensor and the hose and there's no tears or holes.

There is no CEL and other than the rough idle in neutral and the possibility of it stalling, it drives fine, there doesn't seem to be any effect on acceleration.

Any ideas?

Solved:

Turned out to be bad Mass Air Flow Sensor. Replaced and running fine again.

 

So, this will sound kind of stupid but bare with me.


Whens the last time you've checked your oil level? Since Minis burn oil, and recommend topping off between changes (a few times sometimes) that oil level can drop pretty low (love that design!). I would start my car in the am to a weird sound, come up to lights and it would just idle to off from time to time, the only way I could keep it running is start and basically pop the clutch to get it moving immediately.


See if your oil is low, it was my problem and I felt dumb after finding that out.

 

It happened after an oil change so oil level wasn't the problem.

Just got it back from the dealer, turned out to be a bad mass air flow sensor. The reason why it took as long as it did was because there was a whole list of codes when I scanned it the second time and I guess they were trying to determine what was the root cause.