Rx7 Forum and Owners Club - Hi im new and i need some help

Hey guys im new here and i was wondering if any of you could help me out with some questions about my 1990 rx7 gtu. Its an n/a and I am having some idle issues, ive adjusted the idle to 1500 rpms and you could hear it miss. But once i turn the A/C on it drops to 1000rpms. Anyways when i start up the car it starts to rev up to 2500rpm and goes back to 1500. It goes back and forth from 1500 to 2500 i dont know if thats just the rotary engine and how it works or if its a problem within the idle. The other day i was driving on the interstate and it was the first time i got to 75mph. The engine made a rattling noise and sudenly rpms dropped along with the speed it wouldnt let me go over 60 mph. I pulled over to the side of the road and i immediatly thought it was the apex seals, but i looked at the engine and checked everything. There was no smoke no leaks no nothing, so i got it towed back to the house and its able to drive. but if i start to realy push on the accelerator it rattles again! as long as i easily start to accel. it wont rattle. But it never did this before so im turning to you guys who have experience with rx7s and im hoping i could get some answers. Oh and another thing whenever the A/C is on the rpms drop below 1000 when i stop and the car turns off on me. Just another thing to go wrong right, well im sorry this was so long i just dont know what to do. Thank you very much :)