I have noticed on both of my F-bodies, that if the battery voltage is low, the car wont idle, tries to stall. Why is this. I installed a new alternator on one of the cars and it still does it. Once the cars run and drive for 1/2 hour they are fine.

 

Silly question, but have u tested battery?

 

Both batteries are new. Once the cars warm up the idle is fine, in morning (live in florida) the idle is below 500 and they stall. Whats the deal?

 

You are looking at it backwards, The low voltage is not causing the low RPMs the low RPMs is causing the low voltage.

I can not tell you how many times I have had customers complain about low voltage and dimming head lights at idle. The fix is always bump up the idle to factory specs.

With GM alternators once you fall below a certain RPM the voltage drops of significantly. When adjusting the base idle you will see the light get brighter with a 1/8 of a turn of the adjustment screw.

Keep in mind the PCM is digital, you will not see a change in how the car runs until voltage falls to or below 11 volts. If she is below 11 volts she is not going to restart cause the battery is done.