I had this same problem on a Hyundai Coupe about 10 years ago. Everyone kept saying it was the IAC valve but even after replacing that it didn't make any difference. The problem went on for months as it was intermittent. They finally found it was a faulty throttle position sensor. Once they...
I have a 2004 Mazda Verisa that's done 70000km (about 43000 miles). The engine sounds quite rough when it revs, but only when it's cold. After a few minutes it goes away and sounds normal.
I recorded the sound here (sorry just ignore the shaky cam!): http://www.youtube.com/watch?v=frHAUEMFwBg...