Lately my Mountaineer has had a high idle situation that more or less came out of nowhere. I was adding some oil the other day while it was running and noticed that there is alot of vacuum pulling on the oil cap. When I removed the cap, the idle dropped back down to normal. It's not throwing any codes either.

Any thoughts as to what I've got going on? PCV? Bad intake gasket? Other?

 

I can't say that I know for sure there, but the PCV valve is a good place to start. I've never seen a bad intake gasket do that, but it does sound possible...

I hope you'll let us know what you find out!

 

I thought a blocked pcv created pressure and not a vacuum.

 

A PCV valve can fail either by sticking open or closed, and being stuck open is like making a big leak into the intake. It's a simple thing to check in this case; see if the engine idle speed changes when you pull the valve (with its vacuum line) and plug the valve with your finger.