Bad fuel can potentially clog injectors but you would have had to get some really nasty garbage in there. It's possible with the condition of some of the road houses in the middle of nowhere but if the car has spent its entire life in population centers then the probability decreases greatly. I had a project car sit for like 4 years with fuel in the tank, I started it and was able to drive it without much drama to the gas station. Bad fuel really shows its bad when you're asking a lot of it. At low revs or idling it should be able to maintain well enough. Honestly sounds more like a bad Cam/Crank position sensor, failing vanos (which isn't a normal occurrence in the N62), or possibly the MAF. You can easily test if it's the MAF, unplug it and try to start it. If the problem goes away or greatly decrease strength it's the MAF. I just had mine fail (on an M62) and it was fine until one day it wasn't. Drove the X to work all week, got home on Friday and parked it. Went to move it I to the driveway for some unrelated work on Saturday morning and it wouldn't stay running, hunt idle, etc. Pulled the MAF and the rear cover on the sensing unit had come unglued (sealant bead cracked due to age). New MAF in and all problems are gone. Also any sensor circuit malfunction would appear immediately when you put power to it. Not all codes throw a CEL, have to read them with a decent scanner or INPA.

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Again Daily Driven SC'd 4.6iS, whats the point of having a sweet ride if you dont use it all the time.