- OBD2 includes a "learning" capability which will negate any changes in ignition timing you make by spinning the distributor
I have never really seen proof that this is true. I have however, seen evidence to support that spinning the distributor does make a difference.
Doing WOT runs and checking plugs have shown a difference in A/F when going from 16 to 18. Not to mention setting the distributor at all the way retarded causes hesitation and poor fuel mileage.
Of course the best way to test would be on dyno, and not tests that could have deviation or user interpretation, but I choose to keep my distributor at 18BTDC at idle
