RPM's

For manual transmission, if you have a car in neutral and running, what’s the recommended RPM’s for the car to be idle at?

It can vary by year, model, etc.
The specification you should always go by is on the sticker underneath the hood, unless it has been removed or faded/torn to oblivion.

Meh, 1992 Nissan 240SX… Kinda old.
I will probably look for that sticker in the morning then. Thanks.

It varies by vehicle. Typically, 700-800 rpm is normal, unless the A/C is on, then many cars speed up the idle (especially when the engine is cold) to provide enough power so the car does not stall. When cars had carburetors, the cold idle was always fast to keep the engine from stalling. The fastest idle I ever encountered on a production car was the Mercedes 190SL sports car; it idled anywhere from 1200-1300 rpm. If you cannot find a sticker with the number, spend $15 and buy a Chilton or Haynes manual for your car; all the specs will be in there.