I am getting an intermittent fault for "Lean at idle".

I am suspecting an overactive PCV valve (It is the one fitted to the side of the camshaft cover, a common fault)

However, I replaced this particular unit around 2 years ago and the current symptoms are nowhere near as extreme as they were then.

The engine idles fine unless I remove the dipstick whereupon a lot of air is sucked in and the engine hunts.

Now, what I am wondering is if there is a definitive check.

EG, If I connected a vacuum gauge to the dipstick hole, Is there a specified vacuum value for the crankcase with engine at idle?