Rocker box cover ventilation

[Sympol]

Hi,

Currently renovating a 1987 Starlet FWD with 2E-C motor (1.3 liter). The engine blows a lot of light white smoke from the exhaust, but otherwise performs well. I'm thinking valve stem guide replacement, piston rings or worse...

Today I disconnected the hose to the rocker box cover down to the inlet manifold and the motor almost died, was spitting back through the carb but the smoke appeared to diminish. Putting my finger over the end of the hose and the motor calmed down to a smooth idle but exhaust smoke increased again.

Am I correct in thinking the valve in the rocker box cover (a push fit) is the PCV valve? And is there a way of testing this simply?

Any other thoughts on test I could do to check for the cause of the white smoke?

Any thoughts/suggestions/comments welcome. I only have the owners handbook for the car but that is in Swedish (it's a left hand drive model for the Swedish market, where I'm located) and the vacuum hoses/exhaust gas cleaning diagram is not easy to read (see attached)

Many thanks, Sympol