I do need to replace my CCV due to age, but I'm not sure this is my problem - plus it's really cold to take on and extensive job. Here are a couple more test I tried:

The system was already smoke tested and found no leaks, as a test for vacuum leak

• Measure baseline vacuum (-13 PSI),
  Increase rpm to 2500 (momentary increase to -2)
  Back to baseline (-13 PSI) within ~20-30 sec

I then did a test to see what happens of I force it rich and then lean:

• Warm up the car with a drive
  Make it go rich at idle by turning on an unlit propane touch in front of the MAF
  Let it stabilize back to baseline
  Create a vacuum leak by removing oil cap

From the resulting plots, the system seems to respond properly[LIST]
ST fuel trims go to ~ -28 when propane is on
ST fuel trims return to the baseline when propane off
Open the oil filler
ST fuel trims go to ~ +20
Close cap
ST fuel trims go to back to baseline

The fuel trims and from side to side do roughly the same thing
Trying to decide if it's time to take the indy BMW shops advise and replace the MAF - hate throwing parts at the problem since the MAF seems to track RPM fairly well but not sure what else to try beyond doing the whole CCV, DISTA, ICV, etc