Scooby...what was the outcome for you?
I had my car on the dyno today, very standard motor with a nissan timing belt and CAS. no timing cover because I was setting the CAM gears.
This is the trace of RPM from datalogit:
Have a good look at the trace in yellow. it goes from 7700 to 8000 revs instantly and incorrectly.
Now this is not a big deal, it is only moving between 2 cells in the tune so I just worked on an even, broad range in those cells.
I watched the timing belt during the dyno run. There were 3 distinct times that the belt was visibly vibrating, and 2 times in between in ran smoothly. Here is a zoomed out version of the same run from 3000 to 8000
so....this seems very reasonable to me.
Just because not all tuners pick up on...doesn't mean there is no problem. And does it prevent you tuning? Probably not in most cases....it just introduces innaccuracy.