weird warm up

ok first off i have a 86 dx hatch with 234xxx miles with a carb and a 5spd. now the prob... ok when i start my car while cold and sometimes warm it will start and go to 1500rpm or so and just lope. major lope and if i can i will get a sound clip and put it on later but it will but does anyone have any idea??? also sometimes when it goes into high idle it will rev to 3-4k and stay there for like 6 or 7 miles then just go back to normal idle. anyone have an idea on what these problems might be???