Rx-7Blazin

hey i have a 87 N/A and for some reason on accasion it just starts stalling all the time for no reason. it does it when i press in the clutch and the rpms drop, usualy it will go to like 400 then fly to over 1000 then do that a few times then stall and sometimes it will just drop and stall. it usualy does it for like 3-4days then stops doing it and runs fine for a while then it will just start all the sudden. the last time it did this was like a month ago. also when starting cold sometimes it sits at 3k warming up then when the rpm's go down it stalls and other times i statr it and it just stalls. anyone have any clue what could be going on here. I would greatly appreciate it if someone helped me on this,
thanks