Now that you know how the PCV system works, we can talk about some of the problems it can cause with your idle should it fail. I have seen occasions in which a PCV valve came apart internally. In essence, what this caused was a vacuum leak, which can cause all kinds of idle problems.
An easy way to check for this is to pinch off the vacuum supply line to the PCV valve itself. If your engine idle smoothens out when you do this, replace the PCV valve and see if that solves your idle problem. When it comes to PCV valves, the shaking method is not accurate and tells you very little.
As far as Hondas go, if you replace the PCV valve, I strongly recommend using an OE (original equipment) replacement. I've actually seen issues with some aftermarket PCV valves on Hondas, so to avoid this, go with an OE part. Also, Honda PCV valves don't often have problems, and for that reason I don't recommend replacing them as part of a service. I only recommend replacement of a Honda PCV valve if there is an issue with the valve itself.
Some newer vehicles don't have a replaceable PCV valve. These engines usually have a baffle system in the valve cover that functions as the PCV. I've only really seen this type on vehicles in the 2000 model year and up, and not on engines older than that. That doesn't mean they don't exist. The servicing of these systems is specific to the vehicle, so check your service manual on how to diagnose and service your particular system. I'm going to be honest and say that I don't have a lot of experience with these systems, but I haven't seen one cause an idle issue yet. I'll update this article if I do.