Crankcase under pressure?

mvanwey

2 Tacos
'05 Taco, 2.7L
I have had this truck since 2010

Recently noticed that it is idling rough. Started after I changed the battery. (I have no idea how that's related)
Initially, the idle was REALLY low. (300 rpm).

Some of the things I have tried so far (and test again after)
New spark plugs, cleaned the MF sensor, cleaned the throttle body, replaced the pcv valve. I think the PCV valve is what fixed the low idle.

My main question is that when I take the oil cap off when the engine is running, there is a TON of pressure behind it & it spits oil spray all over the engine. I always thought that the crankcase is supposed to be under a vacuum. My understanding is the PCV system is supposed to suck all the blow-by down the intake & re-burn it. The computer knows how much air & fuel is coming down the intake & it adjusts the A/F mixture for the blow-by gasses.

Also, now that I'm looking around, there is a lot of oil leaking everywhere. This has to be because the crankcase is under positive pressure. If I just changed the PCV, why is the crankcase under pressure?

If anyone else has a 2.7L 4 cyl ,please pull your oil cap while it's running & let me know if that crankcase pressure is normal.

Thanks
 
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