colin td5

ive just bought a r reg 2.0 petrol gal and when you acc hard it hits 3500 rpm and seams to rev limiter it self if i on press acc pedel 3/4 of the way down it will rev all the way to 5000 rpm it is fine when you rev it free only under load and it seams to have a misfire as well till about 4000rpm any ideas any 1