Should the crankcase of a 07 Seat Cordoba BBZ 1.4L 16V engine be under vacuum at idle

Jjtoms60

I’m new to this forum or any online forum, therefore don’t know if anyone can help on this matter or point me in the right direction.
My issue is should the crankcase on a 2007 Seat Cordoba (Vin 6L) with a BBZ 1.4L 16V engine be under vacuum at idle, is this normal?
Recently swapped out a BBZ engine (with big end on number 1 gone) for a second hand one. The issue is that at idle there is a little shake in the engine, not a full miss, but when you remove the oil fill cap there is a rush of air in the oil fill cap and the engine stumbles, check engine light comes on, codes “17961 Barometric / Manifold Signal (P1553 – 35 – 00- Implausible Correlation) and 17912 Intake Air System (P1504 – 35 - 10 – Leak Detected – Intermittent). Swapped the oil separator/PCV and the MAP from the old bad engine, same result when you remove the oil fill cap, so fitted new OEM oil separator, same result.

Intake manifold pressure at idle 415 to 440mbar (Vag-com specification say 220 to 420mbar)

Oxygen sensors learning values at idle 13%

I know there may be other issues like other vacuum leaks or o2 sensor, but is the crankcase under vacuum normal, as I’m worried that the crankcase being under vacuum affected the oil pressure on the old engine leading to the big end failing. The BBZ engine I believe it was fitted to the Seat Ibiza, VW POLO and the Skoda Fabia

10-10-20

Generically speaking, yes. It prevents oil-leakage through the seals, etc.
It's created by connecting the crankcase to the air-intake just above the valve to create negative pressure and ventilation of the collected gases.
http://www.motormagic.info/vacuum.htm

Having positive crankcase pressure is a sign of piston ring blow-by, commonly encountered with worn-out engines, or engines with low/high oil viscosity.

Jjtoms60

Ok 10-10-20 thanks for that, I’ll check the vacuum at the dipstick. Just worried that I’m now getting random misfires at idle (not enough to set the CIL)

Jjtoms60

Ok measured the vacuum at the dipstick; reading ½ in Hg, which I believe, is approx ¼ PSI. Noticed that as engine warmed up and the misfires kicked in that the needle on the vacuum meter started to flutter (meter was in my hand not lying on the engine so not engine vibration). When I left the dipstick tube open the misfires got worse. Checked overall engine vacuum 18 in Hg with flutter as above.