>> Look at the hose between the black plastic breather tower and the
>> black intake elbow. It tends to rot and collapse .
>
> Looks OK on mine, perhaps it's clogged internally, does that tend to
> happen?  Seems too large a diameter for that to be likely.

The most likely place to clog is inside the tower, up at the top.
There's a reed valve up there than shuts when there's more than a
certain amount of vacuum in the intake plenum. Given that crankcase
ventilation is shut off at high vacuum, when you're pouring on the
full awesome power of that 2.1, that's the most likely time to see
crankcase pressure. Might want to check your compression. It's not
shooting the stick out, so there'sobviously not a BIG crankcase
pressure problem.

--
John Bange
'90 Vanagon - "Lastwagen"
'90 Vanagon GL - "Wiesel"