how to fix muffler smoke

That poor little car is thirty years old and the engine's probably just telling you that it's worn out. In a couple hundred thousand miles, engines get loose and oil moves through rings and seals and exits the car as black to gray smoke out the exhaust..... A lot of people just live with this until the engine dies. You could do that or just have a mechanic diagnose this and tell you you need a rebuild. You probably won't be able to find a used engine that will improve on this condition, so it'll take about three grand to fix, which is a grand more than the car's worth.