Altima Fast Idle - PCV Valve?

Hi all,

I've got a 1999 Altima 5 speed with 114,000km on it. Since I bought the
car about 2 years ago, it's always behaved as though it was getting too much
air at idle; the idle speed was too high when warmed up (around 1,000 rpm),
and when cold, it would rev up to 2500 rpm which I always felt was too fast.
It also would almost always rev up to 1500-2000 rpm, and hang there for a
few seconds, when I push in the clutch when coming to a stop.

I've since been able to adjust the idle down to normal, and adjust the fast
idle cam on the throttle body so that the cold starts are less crazy, but
the revving up to 1500-2000 RPM when I come to a stop still happens until
the car has warmed up totally, and I come to a stop and give it a few
seconds to settle down to normal idle speed. Once that happens, it behaves
itself for the rest of the drive.

It will also rev high (2000 rpm) and surge up and down a few times when
starting warm, especially if it's been shut off for less than 30 minutes or
so.

The last few days have been quite cold, down to -20C, and both days the
revving up when stopping hasn't gone away even when the car's been warmed up
(or at least when the gauge has shown normal temp). It's also been revving
a little high when starting if the car is still hot.

I'm trying to figure out if the temperature has anything to do with it...
or what else might be letting too much air into the engine at idle that
would account for this. The only thing that I haven't been able to rule out
(temp. sensors, IAC, TPS, MAF test fine, and no sign of vacuum leaks) is the
PCV valve; does this seem like a possible culprit if it's sticking open at
idle speed for a few seconds, or sticking open and the ECU is trimming the
idle down eventually to compensate?

I've had my autotap connected on these cold mornings and the coolant and
intake air temp sensors seem to be fine, so I'm thinking the problem may be
mechanical and not electrical...

Any suggestions would be great, otherwise I may have to wait for the next
cold snap and try to get into the dealer with it...