Look more like smoke or steam?

It looks like smoke

I do not think this has anything to do with the idle of the car!!  Smoke in the valve cover??  Could it be just "hot" oil?

Smoke coming out of the PCV is just blow by..unburned gas still in the engine..the PCV sucks that has out of the crank case and burns it in the engine..the valve needs to rattle when you take it out..if there is any question that it is bad replace it..check the hose right at the base of the carb..it could be torn. If it is really hard replace it..use a good hose clamp also..all (for the PCV)..if you get a ton of smoke coming out of the PCV hole you may also have worn rings..a wet compression test will tell you that..probably not a big deal..WITH a fire extinguisher next to you..spray carb cleaner around the base of the carrb..if the idle changes the carb or gaskets are leaking..setting the timing and idle mixture and idle speed is an art..they all affect each other..if you turn the idle screws all the way in and the car doesn't change idle the carb needs rebuilt or the primary needles are not in right..LMK.
Rich

Also, check the PCV valve itself and the breather going into the other valve cover. Basic tune up stuff that will prevent the engine from breathing well if neglected over the years...

You are describing blow-by.  It is normal for an older engine.  As the rings wear a little, they leak a tiny bit of compression into the crankcase.  Since your crankcase is full of splashing oil and vapor, adding hot compression gasses burns a very small amount of that vapor and blows it out any opening.  Rich is is correct that the PCV normally sucks it out so you don't notice it.  Unless there is a column of smoke, don't worry about it.

Larry