Slight Sputter on Cold Start

On cold (<40 degree) mornings when I start my G20, it will sometimes sputter slightly (<1/2 second) as it comes on. It will also from time to time rev to about 1550 or so on cold start in the morning, quickly down to about 1000, and then quickly back up to 1500 with no sign of an impending stall. There is no other hesitation or anything in the engine. It doesn't do this at any other time of the day, not even when I start it in the late afternoon to go home after having it parked all day. Once warmed up it'll easily go to 5000rpm before shifting, and would go higher if I pushed it. I'm having the car in for some service on Wednesday anyway, so is there anything I should have looked at that could cause this problem? Bad tank of gas maybe?