If the RPM's are getting low enough, this is normal and the alt is fine. However, what is causing the RPM's to get that low. Check for vacuum leaks, check idle air control valve, check fuel pump pressure.

Answered by Jacobandnickolas (expert)
57,318 answers provided

Thanks Jacobandnickolas, would you know what the proper setting should be for the RPM's after it has warmed up and I'm in drive and sitting idle? I have conflicting answers. It seems that the RPM's are about 600 to maybe 700 or so. I can't tell that well due to the fact that there are only 500 line increments on the RPM indicator. Even when the truck is idleing what looks like to be very low, it seems fine. Meaning there is no shaking or rattling at that low idle. The truck is running smooth. Thanks for all your help. Can't figure this one out....

Response from MazdaOwner
1 question asked

700 sounds right.

Answered by Jacobandnickolas (expert)
57,318 answers provided