1988 Chevy Corsica wont idle sometimes

Ok, here it is, my friend bought the car it ran good, he did the plugs and it ran like crap, I bought it from him and did the plugs again he messed up the gap size, so know it starts right up, idles about 1000, but sometimes the idle goes up then down, then it would stall, and wont start, I give it some gas it starts and idles fine, go to raff it up and it does the some thing, raffs up then down, and blows out smoke, my gauges say its running very rich, what should I do