I have an automatic 2007 Mazda3 and it has a starting problem I can't find the source of. When I do a cold start, the RPM go to about 2500, the car sputters and almost dies as the needle drops below 1000, then the RPM goes back up. Occasionally while warming up, when the RPM hit 1000 it will fluctuate by dropping below one, slightly go up, slightly go down, etc. until I put it in gear. It's got about 32k miles and I've taken it to the dealer since it's still under warranty but they couldn't find a problem either.