Smoking, loss of power, have been told its the inlet manifold

going to cry, just sold my alfa with engine management problems, purchased a saab 1.9 turbo diesel, 2004, 150bhp. Noticed it had been loosing power under load and smoke coming out of the exhaust and under the bonnet and diesel consumption reduced. Had it towed away to a garage that said its the inlet manifold and will cost me about £5-600 to fix. Is this right or could it be some other fault?, I have had no lights on the dashboared showing any faults, having owned alfas for years I should have learnt my lesson. Im car-less unless I pay this to have it fixed, quick responses would be very much appreciated. Thanks, Ruth