Automatic Idle Adjustment One Person HOW?

“I also run an idle solenoid so that I can set my in D idle rpms differently than my N/P idle rpms. I like to keep my N/P idle rpms lower than my in D idle rpms”

What is an idle solenoid? When I drop into gear and it’s under load I always drop RPM’s. This is fundamentally why I started this thread. You seem to be able to avoid this and I want to understand how….
Lotta carbureted cars in the 80s and 90s used throttle solenoids for rpm control when the AC was turned on.

Standard Motor Products ES9 Standard Motor Carburetor Idle Stop Solenoids | Summit Racing