Most valves should rattle a bit when you shake them, indicating the plunger is free.
The PCV system is one of the earliest/first emissions control features offered. It works by drawing combustion blow-by and vapors in the crankcase back into the intake for combustion rather than freely releasing into the atmosphere. An additional feature is that it helps keep the oil cleaner longer.
The valve is lightly spring-loaded so as to be shut with the engine off or at very low vacuum levels such as WOT take-offs. Sufficient engine vacuum will pull the valve open and draw blow-by from the crankcase into the intake. This air removed must be replaced somehow, or else the crankcase would approach the vacuum level of the intake.
In our case, this replacement air is drawn in through the tube you mentioned, being filtered in the air filter enclosure. Some vehicles use something as simple as a screened mesh on the oil filler cap or parasite a filtered feed after the main air filter.
Some notice that the PCV air filter will become oily. Suggest this is due to a downward slope of the tube, allowing condensing vapors to run toward the filter, or perhaps excessive cylinder blowby overcoming the capacity of the PCV system.
At any rate, suggest to either clean or change your PCV valve, inspect / change the filter as needed, and you should be good-to-go.
1989 F150 XLT standard-cab shortbed 4x4, 5.0L, AOD, 3.55 gears, manual hubs, 31x10.50 tires, 218K miles. Repainted Oct09. SOLD - Jan2015
2014 F150 XLT standard-cab shortbed 4x4, 5.0L, 6-speed auto, 3.55 gears, auto hubs, locking diff, trailer pkg, 5K miles.