I have a 2004 Mazda 3, and the battery was finally done after six and a half years. I learned some new things about “newer” cars (my last car was an ’89 pickup) and I thought I’d share. This may only apply to Mazda 3, since in the forum-reading I’ve done it sounds like people are a little surprised at the way the Mazda 3 behaves. So here’s what I’ve learned.
When you disconnect the battery in your car, all the electronics reset. That makes sense. What you may not know is that the computer in your car also resets itself. In the case of the Mazda 3, this means the computer has to relearn how much fuel to give the engine during idle. So for a few days your Mazda 3 may rev between 500-1200 RPM when idling at stop lights. It’s a strange experience, but after three days my car is back to normal.
I’ve heard (although it didn’t seem to help me) you can try assist the car in learning the idle by starting it cold and letting it warm up without touching the gas. I attempted this and it didn’t seem to affect things – time only solved my problem, but your experience may be different.
Additionally, the computer in the Mazda 3 does need to be updated from time to time, and I believe you can take it to your dealer to have the computer “flashed”, as they call it. All they are doing is updating the firmware on the computer to the newer version from Mazda. This may also help.
So if you’ve changed the battery in your Mazda 3 and you’re worried about the idle, wait a few days. There may not be a need to start taking things apart, replacing air filters, and cleaning throttle bodies (as I’ve seen recommended).