I have a growing problem with excessive crankcase pressure in my 90
240.  I checked the usual suspects: the flame trap and hoses.  All
were clear.  I assumed the "breather box" was clogged or severly
restricted.  I replaced the box and everything above it with new
parts, just to be on the safe side.  I removed and checked the nipple
on the manifold. It was completely clear.  The care still fails the
jiggle test miserably.

Oil had been leaking out onto the valve cover from the filler cap.  So
when I replaced the PCV parts, I also replaced the brittle filler cap
seal with a new one.  Now I am concernced that, with a good filler cap
seal, the pressure will have to find another outlet---like the rear
main seal.  And I don't want to blow that or any other seals as a
result.  I blew the rear main seal once about four years ago, and it
wasn't pretty (clogged flame trap and hose leading to manifold
nipple).

I wondered if the problem could stem from insufficient vacuum. I
checked for cracked vacuum hoses.  They all seem to be in good shape.
I don't have a gauge (yet), but I do feel vacuum in the various lines
if I place a finger or the palm of my hand over the end with the
engine idling and at higher rpm's.  It's the same at the intake
manifold nipple.

The throttle body has some carbon buildup around the point where the
main hose connects.  The hose itself has engine oil in it along its
length all the way down to the Air Mass Meter.  Obviously oil is being
forced where it shouldn't be.  I considered removing the throttle body
and completely cleaning it. Is there a chance that carbon/oil fouling
within the throttle body could be reducing the vacuum in any way?  I
do, however, feel vacuum at the manifold nipple at idle...

The car idles somewhat roughly and is much noisier than it used to be
several years ago.  I have never done a valve adjustment on the car.
I've had my 240 for seven years and have added approximately 40K miles
since then, bringing the total mileage to about 160K. Can poor valve
clearance cause excessive pressure?

Any ideas?

Thanks in advance.

Zeke
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1990 Volvo 240 Sedan
Pittsburgh, Pennsylvania