Ok I made sure to conduct a search but the only thing I find idle wise is for high idles, and not low ones. It started recently, on my 84 rx7 gs. After the car is fully warmed up it usually bounces around 700-800 rpms, but as of lately its been around 400-600 rpms and I don't know why. It feels like the car pulses (like it normally does) but does so in a way that the rpms drop down to 4-600 and stay there until I accelerate. It doesn't affect driving too much aside from the pulsing, and none of the searches I've conducted have helped to diagnose a low idle issue. I am new to rotaries and I've never been mechanically inclined, but I loved the car so I'm willing to learn as much as possible. Anyone who can help out please give me some detailed instructions, especially if I need to find a part I'm not familiar with. Thanks in advance.

Assuming a recent tune-up was done I'd say vacuum lines might be the culprit. Do you hear any "whooshing" sounds in the engine bay? Take a can of starting fluid and spray around the lines and see if the idle jumps/drops. You could have a crack in one of the lines. Also, one might have just come off. My friends GSL-SE did the same thing and it was line running from the back of the throttle body to the top of the rear housing. We plugged it back it and now it hovers at 800.

Besides what satanic stated. Check the operation of the shutter valve. Is there an abnormal honking noise coming from the air cleaner area?

also there are 2 coolant o rings which die in and then soak the intake gasket, which then leaks vacuum...