Cold engines idle high, 1,000rpms or so
700rpm after warm up
I assume that's not it?
Engine warm and idling
Pull off the PCV hose and plug that port with your finger, if RPMs drop it's leaking
Do the same with any vacuum hose connected to intake, pull it off and block that port
Yes, PCV valve has a weighted valve inside
When throttle is closed, intake vacuum is high and the weighted valve is pulled up by vacuum and closes off the hose to intake
As throttle opens vacuum drops and so does the weighted valve, pulling in "air" from valve cover and crank case
The "air" in the valve cover and crank case areas is Blow-by, basically exhaust gases
When a cylinder fires some of that explosive pressure "blows by" the piston and rings, hence the name blow-by, and its made up of exhaust gases, it ends up in the crank case which is connected to valve cover areas by the oil drains in the head(s)
PCV system was added to suck out the blow-by and re-burn it in the engine
So its an emissions system
Just FYI, blow-by gases are hot enough to Vaporize oil, and they do vaporize some of the oil coating cylinder walls and piston/rings
That's the only place in an engine hot enough to vaporize oil
So the oil vapor can also be sucked into the PCV Valve and intake
As any engine gets older blow-by increases and so will oil vapor,many add Catch Cans to reduce the oil vapor being sucked into the intake
The Breather hose is to let in filtered outside cooler air to try and condense some of the oil vapor inside the engine, but also serves as an Overflow device if PCV Valve isn't working
Blow-by(and oil vapor) can exit thru the Breather and into the air plenum and be sucked into the intake via throttle body
If throttle plate has a oil coating that is whats happening or there is way too much blow-by