Alternator problem???
 

My 1984 targa 911 alternator doesn't start charging until I rev the engine over 2k rpm. Then it's fine . It works fine If I shut it off the same thing happens. Again all the time . Not charge on idle Any recommendation or test ? I'm not good on mechanics

Time for a rebuild

Most likely the internal Regulator brushes are worn down.

Remove Alternator and remove regulator, I bet the brushes are gone.

If you have AAA, have them check the entire charging system and give you a print out for your records.

Bottom line, it is time to remove and rebuild or replace the alternator.

Does the light turn on - key on engine off?

The alternator was rebuild 3 years ago. And the regulator new. The light don't turn on with the switch ok or without a key. With key in on engine off yes turn on

So under (ab)normal operation, you turn the key on and the alt light is lit. Start the car and the light goes off but no charging. Rev to 2000 the car starts charging and light is off and never flickers until restart?

My alternator the slip rings were worn down with grooves about 1/8 of an inch. The first rebuilt one I got also had worn slip rings. I don't think you can source the slip rings to rebuild this Valeo alternator. I notice they are now available new for about $300 which wasn't the case a couple of years ago.

i stars the car and no charging. Rev to 2000 the car starts charging but I to check the light is off and never flickers until restart?

Numbers? at 2KRPMS, what is the voltage? flickering is not good thing, She is trying to warn you before you get stranded out in the street.

Start on idle no charge, then raise to 2k rpm then start charging at 13.8v approx and maintain that voltage on idle, after that works fine all the time. If I turn off same problem again every time

When I had my alt rebuilt, the new regulator they dropped in went bad on the 3rd day, had to return and they dropped in an upgraded regulator at no charge. Lucky I have a life time warranty on the rebuild.

Zero issue since. Next time bench test the alternator to insure it is working properly. It is allot of work to reinstall it.

Check your grounds. Sounds like you may be overcoming resistance. But do bench test the components I agree rebuild may be subpar.