Sounds like either a sticking IAC valve or the infamous intake gasket leak.
When checking for an intake leak, the testing must be performed when the
problem is occurring. We see techs (that should know better) trying to find
such a vacuum leak on warmed up engines... since thermal expansion has
helped seal the leak, you can imagine the outcome...).

For your fuel filter... dirt and small pebbles can find their way into the
fuel line connection. This stuff will keep the tool from expanding the
retainer spring far enough to release it. Tapping lightly with a screwdriver
handle os such can help dislodge most of it. Also, rotate the line on the
filter to help break the O-rings loose and, if necessary, a wee snort of
penetrant (on the joint...) can help.

I spend 90% of my time working on diesels so I can't help with PCV
location... at least not by "foggy, old man memory".

The PVC is on the back on the engine (firewall side).  Almost impossible to
get at...