Didn't change the oil for 20K then oil light came

You dont need to change you oil ever 3000 miles oil companies just want to make more money off use poor saps..dont get me wrong...if its a new car you should change it more frequently because its still going through a break in period...as the car gets gets past a break in point about 60k oil no longer has to be changed as often normally 9k or 10k should be sufficiant and especially a car with 130k is broke in as its ever going to get...oil doesnt wear out! it just get dirty! as long as you have oil in the engine it should run o.k. i"ve always added slick 50 in all my older vehicles...it helps gas mileage (2-3 miles per gallon more and my car has 293k on it and still has the same starter...the additive makes for easier start-up causing less wear on the starter when it cold. as far as the black smoke..that usually means a fuel problem running to rich...try changing spark plugs/wires and smog sensor and to help insure you always pass smog change the catalytic converter.

To burn BLACK smoke then you have a diesel car as engine oil burning in a petrol will burn BLUE unless you dident change filter and air filter but it should be blue if so then .....
Rings have broken or stuck in groves in piston and bearings would make a rattle on starting ..
check out colour of smoke Blue is oil
White is WATER , black petrol but dirty filters all..

Black some is from too much fuel, blue smoke is from burning oil. Keep an eye on oil consumption now. If your check engine light doesn't come on, just keep an eye on it. 20k miles??? Dude!