With the engine running..I take the unvented oil cap off....the revs immediately
pick up....if I take the hose to the PVC off the revs pick up......so is the PVC
not working?

That means it is working.

So what suppresses the idle.....crankcase pressure?
And at what revs should I expect the valve to open?

The valve is open, that is why the idle increases.
If the valve was closed the idle would stay the same.

The idea is to keep the cranckcase pressure low or even a partial vacuum.

Does your car have a sealed oil cap or a vented oil cap? I think it should have a vented oil cap.
The vented cap lets clean air into the crankcase at a restricted rate.

It has a sealed cap.

I have used PCVs with sealed caps and filtered caps, they usually work OK with either.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The only possible problem is if there is too much vacuum and it sucks the rocker cover gasket in (like it did on my old Torana)

My 1310 does the same thing , has done so for 10 years, nothing to worry about.

Colin

Keep an eye on the rubber diaphragm in the PCV valve. The ones they sell now go hard in a few years, then the valve can't work properly.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I've heard crank seals make strange noises due to too much crank case vacuum.

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Dean Hutton's first car was a Mini.

I disconnected and plugged the PVC and vented the vent to the atmosphere.
The car ran much smoother and the idle more stable.
The downside was the fumes.....I think I got lung cancer from the trip.
There has always been a nice sheen of fresh oil over the southern end of
the head and block.
It would seem presure is building up in the block.
So one would have to think there is problem with the PVC.....wouldn't you?

What was the problem in the first place?

Well I didn't know there was a problem...It was that I noticed the idle picked
up VERY noticeably when I took the oil cap off.....and thought that can't be
right. When I unplugged the PVC the same thing although the revs picked up
it was a bit rougher, obviously sucking some air but not enough to stall.
I could never get a good idle.....blamed the carbies......but now I get a good
idle.

if it aint broke > if you go looking for faults you can usually find them

I think it was broke....I just not smartyenuff to know