I've gotten more or less used to the above normal idle on my 99 Altima... it seems to be more consistent now than when I first bought the car, and it's lower due to a "restrictor" I placed in the tube that diverts air to the AACV valve, but still a little higher than spec. The strange thing that I've noticed is that, during warm-up on cold mornings, just after the temp. gauge reaches the normal temperature mark, the idle is exactly where I feel it should be, and where it is on my '94 Altima. But, after driving a while longer, it starts idling higher again, and stays that way.
I'm wondering if there might be any easy (magic) explanation for this... maybe a problem with the coolant temp. sensor, or the thermostat acting strangely? The car seems to take longer to warm up than my 94 does, and normal temp seems to come more gradually instead of almost all at once as in my 94, so I wonder if the thermostat may be sticking open a bit and slowing down the warmup a bit (and maybe preventing the car from warming up completely?). The other thing that may be related is the car will stumble very slightly when I moderately tap the gas pedal from idle. The revs will actually drop from where it was idling for maybe 1/2 or 1/4 second before it picks up. It doesn't happen with slight nudges of the pedal. Maybe that's just a peculiarity with the programming of the ecu in this model.. my 94 is very responsive in comparison, and wants to rev the instant you touch the pedal.
Does any of this seem related? I'm just throwing the question out there, so whatever ideas anyone has would be nice to hear.