P0015 and stalling

[M5Guy]

So our 08 X3 with only 110k miles runs great 99% of the time, but once in a while it will stall when coming to a stop. Otherwise plenty of power and good gas mileage.

I've had a P0015 code, so I replaced the cam position sensors and VANOS solenoids (very simple job). Cleared the codes, drove, still stalls, and the code came back.

Reluctantly took it to a local independent BMW shop hoping they had better diagnostics. They said "you have a P0015 code and we would like to put in new VANOS solenoids for $700".

So that was a big waste of time. Any suggestions? Oil is always clean and th car runs like a champ otherwise. Some might be inclined to suggest gas filter, etc, for the stalling but that would not explain the code.