Voltage dropping too low at idle
 

Lately I’ve been noticing if I have my AC on and idle at a stoplight, the car voltage drops to 11V, and my tach needle starts dancing. As soon as RPMs get above 1000 or so voltage climbs above 12 and it seems fine and charges fine at ~14V on highway. Does this mean my alternator is getting weak, or is this some other voltage regulation problem? This is a relatively new issue.

Check condition/age of the battery, also is the pulley belt tight?

It’s certainly a good sign that the charging voltage goes up to 14 where it should be. I suggest checking your grounds. I just replaced the transmission to chassis ground and it made a difference for me.

drive the car to some place like advance, they will test it for FREEEEEE and tell you what is wrong.

Battery is pretty new. I notice if I turn the AC off, it can maintain adequate voltage even at idle. It’s just when I have AC on & idle where the problem appears.

Could be the VR, could be the alternator on the way out, could be the system is just overloaded at low rpm.
As T77911s says. Only one way to properly diagnose - with the right gear.
Alan