Vauxhall Corsa really low revs

ive got a corsa 1.0 r reg ,i have to rev it when i start it to get it going not always but most of the time,its jumpy in low gears and i have to dip the clutch quite a lot otherwise it shudders it also seems to pull forward sometimes when im going 30 in 3rd without me accelerating.when its idle it soundslike a bus and like its about to give up.some times its more noticable then others.is there some way i can adjust the revs?ive just paid out to get exhust done so am hoping its not too bad!its had so many problems already.