I recently bought a 1988 N/A rx7 and sometimes when I start the car it fires up perfects and runs completely fine. At other times when I start the car the revs drop from 2000 right to around 500 and then the motor shakes violently and stalls. Will start and die out like that for a few times and then eventually start completely normal again. If anyone has encountered a similar issue or has some idea what the problem could be please let me know. I will try and get a video the next time it happens.

 

if u have a timing light, the next time it runs rough like that connect it to each bottom(leading) plug wire to see if there is spark at the plug. my guess is that for some reason it starts running on one rotor. although, u will need to work the throttle to keep it running.

 

the timing light is a good idea. the other thing to check is the basic idle settings, these cars have an idle speed, idle mixture and throttle sensor that all are adjustable.
so when its warmed up set the idle speed, mixture, and TPS, and it might help it when its cold