Idle rising on cold startup?

A&Q about 350Z
Q:

The 16v is running a treat at the moment, and there's just one niggly thing it does, and I'm not even sure if it's a fault:
When you start the car from cold, it jumps into life really nicely, then the revs rise on their own up to 2000-3000 revs and come back down to normal idle. Is this just the cold start valve working it's magic?
A:

they should rise a little...not 3000 though
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