2000 Mazda Protege rough start

2000 Mazda Protege 4 cyl Four Wheel Drive Automatic 90.000 miles

2000 Mazda Protege starts at first key but for the first few minutes idles roughly. It feels like a fluctuation that is made very clear if I turn the ventilation on. It goes up to 1500 rpm only to slowly return to about 1000 or 900 rpm, where it then stays. Once the engine warms up, no other problems are apparent (is fine at stops). It appears to act like this only with a cold engine. The acceleration valve has been checked and is clean. No warning lights as of yet. I would much appreciate help with this problem as nobody has been able to figure it out. Thanks.