I have an 81 12a that I just bought recently I am trying to get it on the road but am having a few problems. I just changed the plugs and wires as well as the air filter and the choke cable. With the choke out the car is idling at 3000 rpm for about 5 minutes then the choke goes in and the car shuts off - I start it back up and play with the gas a little and had it idling at 800 rpm for about 3 minutes and then she sputters off. after that I can start it but it shuts off as soon as the rpms drop below 1000. any suggestions would be appreciated. ( it wont idle cold or at operating temp. )

 

I'll bet it's a vacuum leak. Take a look at these search results pertaining to the shutter valve and judge for yourself if it sounds like this could be your problem.

Good luck and welcome to the forum!