1995 Chevy Blazer ERG Valve & Brake problems

Hi..i took my blazer to a local mechanic because it was idleing roughly and had lost braking power especially going downhill. He said he put it on a diagnostic machine which said the EGR valve needed to be replaced. He said he couldnt get this valve for this old of a model and said he would just clean the old one...it did ok for 2 weeks but now the problems are back and the brakes now have a vibrating grinding quality to them when going downhill...what should i do?..ty for your kind assistance, anna