[E93Dude]

I walnut blasted my 07' 335 a few months ago, and also had a slightly rough idle for a few weeks/couple hundred miles until it smoothed out. I suspect it had to do with the ECU recalibrating to the new airflow paradigm. Interestingly, even in that initial rough idle break-in period, I noticed better gas mileage once the car was warmed up. I'd give it some time to see if things smooth out.

The MAP sensor should be cleaned since its in the same airflow as the recirculated fuel/oil/air mixture from the PCV system. Its located on the top of the plastic manifold assembly that had to be removed to do your walnut blast. The MAP can be removed from the top of the intake manifold by with a couple of screws and cleaned with cheap MAP/MAF cleaner from any autoparts store. With 135K on your odometer, you should definitly clean it.