fiesta is shaking as soon as i turn ignition on?

i have an old h reg fiesta but recently it has just started to shake all over and make this horrible sound... you know like the really really old cars sound or like a tractor. now it has only just been through an mot, the fluids and everything are fine. it did something similar a couple years back and it was clogged up oil in engine, i looked this time and there was a little bit but i cleaned it off and still exactly the same problem. it is well looked after and i want to fix it asap as i can't really drive anywhere like it.. please advise asap if can help