All I can say is take a deep breath, and have it looked at by a mechanic tommorrow. We can give you all the advice in the world on what it "could" be, but based on your limited knowledge I wouldnt go tearing things off and replacing parts. Contact the seller, tell him its F!!@# up from the very beginning, and that you want to take it to a mechanic and have it looked at, see if he is even partly willing to refund you your money. If not suck up the inspection cost and find out exactly what is wrong with it. A mechcanic can tell you, we can't. Your putting 1.3k + buying this car may as well spend 20-50 dollars having someone tell you what the problem is and to see if its a big deal or just something small.
BTW, 99% sure the guy knew something was messed up and thats why he sold it for that price, I think I saw you post earlier asking if this was a good deal, and everyone said yeah if there isnt something majorly wrong with it
Best of luck friend, but take it to a mechanic and figure out exactly whats up