Classic/Antique Car Repair: car idle, 1977 chevy impala, chevy impala

Question
I have a 1977 chevy impala v8 305. When I turn my car off it keeps runnig for a second and than cuts off. and when I turn it on it runs like my foot is down on the gas but it is not. How do I lower my idle?  

Answer
HI Steve;
   Well there  is  a small  adj. screw that is on the linkadge arm - with the air cleaner off you will see how the set up is - on the drivers side of the carb. the screw only has to be turned a bit for it to be lowered, but if it was fine prior , than there is a reason for the hi idle , it could be the choke , or dirt , etc. so give it a good look see first ok.or even  a spray with some carb. cleaner .