I have been working on 81 12a rx7 project for about a year now. Its been driving good for the last 6 months or so, haven't changed anything in that time. but now every once in a while after the choke pulls in the idle will drop to around 500 rpm or less (normally its at about 700 or so). wondering what is causing it, its low enough that the car acts like its about to die.

 

Its still cold and not completely warmed up when the choke pulls in. Thats my guess since its
now winter everywhere.

 

but it will be doing fine then randomly when i stop sometimes it just decides its going to drop....its not the second the choke pulls in its later

 

Have you tested all of your emissions equipment? It sounds like a vac leak but that would be a constant problem not intermittent like you described. That leads me to think it may possibly be emissions equipment related, such as a bad or failing sylenoid.