When you drop the Rpms fast engine will stall?
 

I have a 1988 rx7 non turbo and when I first got it it wouldn't idle. But now that's not he problem. Hot or cold when I rev it to anywhere past 3000 rpm and drop it rapidly the engine will stall?
Also sometimes when it is hot it is rev hunting between 1200 and 1500?
I need help ASAP. Thanks