Anyone ever run crankcase at vacuum?

Well, those are the ones I am talking about. We tried an old one and a NOS one on 14-15" vacuum and neither one shut down properly to the lower volume idle air flow. If you knew your actual vacuum level at that time, then this could be known or rejected as a possible cause. But I am sure that is a while back!

We went to a lower vacuum PCV on my son's 340; it is from a GM v* 4 BBL application (FV191) and shuts down the flow properly at that vacuum level. Sure makes the idle better.

Your trick is kinda the same as a restrictor in the PCV system than some guys do on really low idle vacuum engines.