I bought a fiat brava 16v 1.3 litre engine?

back in march. At first it worked perfectly but now whenever i turn the ignition it revs by itself. i just sit there with my feet on none of the peddles and it happily shoots upto 2000 revs by itself. Also when i change gear or go up a hill it over revs and barely moves- especially up hills when acceleration is needed. i spoke to a garage and the man said its a problem with thew cars computer(???) and that he would need a new computer from another fiat brava along with the keys. Does this sound right. When i first bought the car it was great but this is really doing my head in now. I can take the reving by itself cos its not a problem if im in 3rd/4th gear as the revs will be that high anyway but the over revving and revving when im in 1st gear is a nightmare - ANY help much appreciated as im clueless when it comes to cars - CHEERS