Something I wanted to share with anyone reading my "journal"... I've had a persistent 2E91 CEL that would not go away. I received it about a month after I installed my downpipes and Velos stage 2+ tune. I gave everything in the engine a once over, found the vband clamps on the downpipes were not tightened down all the way, found one of my hose clamps on my custom intakes wasn't on the coupler completely etc. I had the car smoke tested, reset adaptations, my injectors tested, spark plugs, O2 sensors all checked and tested. I removed the tune, it still came back. My code was particularly odd since it was showing up by itself, and reporting lean. Usually this code is accompanied by another code pointing towards a vacuum leak of some sort. To add to the strangeness of it, I'd get the code when just cruising at low RPMs, not when I was on it or driving it hard. If I clear it, it would come back within a day or two, about 30-40 miles... Reading online, there wasn't much on this code alone, and less on an X5M, but I was able to piece together some info.
People complained of this code during winter months, or when they used certain tanks of E85... I dismissed this for a few reasons, I run 93, always from the same gas station and there is no ethanol added... or so I thought. I went to get gas a few weeks ago, and noticed that it was now showing that they are using 10% ethanol. I went inside and asked and they said that starting in the fall, they begin running some ethanol in their 93 as well, then switch back to straight 93 in the spring. I don't know why exactly and the attendant didn't either. Keep in my my code started around the same time the ethanol content changed.
The other thing is that for the past few tanks of gas, I've been running an additive as well. I've read so much good about the additive that I bought a 4 pack and figured I'd put my car through a "cleanse"... The product is Liqui Moly Jectron Gasoline Fuel Injection Cleaner-pk4
https://www.amazon.com/dp/B00LPV1LHE..._WnHbCbBTYMHJN
I read about someone getting this code when they put an injector cleaner in another BMW model, so a light clicked on and I hadn't used the last one to see if that could be causing the fault.
I ran my gas tank basically dry, I had about 25 miles left to empty, found straight 91 at a gas station nearby and went and filled up. Check engine light went off on its own and hasn't come back. No code anymore. Unfortunately due to these two things being a factor, and stopping both at the same time, I don't know if it was the ethanol laden 93, or the Jectron...
Anyway, this fixed my issue and I wanted to share my info in case someone starts receding the same and is tempted to chase it with parts as it's a pretty generic code.