1993 Toyota Tercel tercel shakes badly when idle wont go pa

I have a 1993 toyota tercel DX and I was driving it on the highway the otherday and it eas going along just fine.then it wouldn't go past 45mph all the way home.also when it idles it idles very rough like it is only running on 2 cylinders.it also smokes badly out the back and underneath the car.I replaced the sparkplugs and changed the oil but it still didn't help it out a bit.I need to know what could be wrong I dont have the money to replace the engine.Also I live below a steep hill and I had to try 3 times before it would go up the hill.Pleas I need an answer ASAP. this is the only vehicle I have and I need it for work.