An update on my odyssey. As I feared, getting the correct hoses is a problem (of identification). The two I received yesterday - after lengthy phone researches with a parts house - were incorrect. I also received the OVP and replaced it - no time to hookup to and monitor the output from the old one. Since I was in the neighborhood, and all else had failed, I removed the entire hose assembly from the output of the idle air valve, to study its function and get part #'s.
As you can see, there are three hoses connected together, the part #'s embossed on them. The plastic connector between 19 87 and 21 87 is an ordinary barbed tube. The one between 21 87 and 43 87 has more elaborate plumbing, but no moving parts. It contains a shaped funnel terminating in a small hole - the metered PCV orifice mentioned in other posts, and the only opening between the hoses. The small port visible at right angles is open to the 'breather' side of the assembly, and connects to the pressure regulator safety port.
The hose I need to replace is the 21 87. All three look similar in the photo, but the end hoses are new, compliant, and seal well onto the plastic connectors. The center one is old, hard as bakelite, and certainly brittle. It no longer grips the connectors tightly, and certainly will leak air some. I could not remove it from the connectors without fear of breaking it.
Other old rubber in equal need of replacement are the bottom of the air flow meter plenum, which I received the correct part I believe, and the hose from that to the input of the idle air valve - and that was the other incorrect hose. The latter part I still need to identify somehow, but I won't pull all THAT apart until I have the new hose in hand.
Anyway, idle and drivability were on good behavior for the drive in to work today, so the OVP may have been the main component causing the problem. Since intermittant, I'll give it some time to make a positive judgement.