Need some help.....2001 civic

I just bought a 2001 civic 2d 5sp. The check engine light just came on and the oil light comes on and off. My rpms won't go over 4000. Was wondering if anyone else has had this happen and why?

Was it new or used?

It was used...2001 with 14000 miles. Today the engine blew, the dealer forgot to put oil in it after they did the oil change before they gave it to me. So now I have a lawyer and a car that I've had for less than 12 hours with a blown engine( the dealer said it might not totally be gone, but it makes a heavy knocking inside the engine.)

That really blows man. That is all the dealers fault, I mean come on a brainless monkey could remember to put oil in a car after it drains it. Thats the whole point of an oil CHANGE, New in Old out. I hope everything turns out good for you in the end.