roll back on steep incline was norm, on my 99cdx. The car in my experience will not account for holding on any given slope. It would roll forward at between 4/5 mph on flat, with both feet off pedals. If you where to drive it up an increasing incline it would come to a point when the slope would b enough for the car to come to a halt, if you drove further up to a steeper part it would roll back to a point that tick over would stop it.This will vary with your tick over problems i am sure. I had constant agro with my icv after it packed up(car stalled) had to remove and wash out with carb cleaner 5 or 6 times to get working again, and once a month to keep on top of it. Did not notice any prob.with a fault code if left un plugged, just plugged it back in.
The rubber bit to plenum never fitted well
So wrapped electrical tape round the ribbed bit to keep it air tight, and replaced it every time i cleaned it. Front multi ram
on myn stopped working koz i got the vac pipes wrong way round at the bottom of bag pipes(air intakes). Easy done. If you notice a step at 4k rpm try swapping the pipes around on the vac tank(if it has one, see guide) at the bottom of bag pipes? Should be able to see it working by blipping the throttle from the engine bay. Ttfn.