Will this stem fit a 2003 kona coiler?
Unless they released a version I am unaware of, the Coiler has a 1 1/8" head tube, headset, and steerer tube. So yes, this will fit the bike. But chances are the handle bars that came on that bike back then have a 25.4mm diameter clamp zone. If that's the case, you'll need shims or new bars, probably new bars.
One more thing....I think 04 is the first model year that the Coiler was available. Could be wrong, I just tend to remember worthless info like that. Lemme know if I'm wrong.
To add to the other response: Yes you're right, 2004 was the first year the Coiler was out. And..it came stock with a Marzocchi fork, so the 1 1/8 steerer tube is correct.