MVA emmision test diagnostic fixes?

i own a infiniti i30


i took it to the emmision and i got the response bellow:


*p0400 exhaust gas recirculation A flow


*p0325 knock sensor 1 circuit bank 1 or single sesor





i was talkin to a mechanic and they were talking about 400$ of repairs..





i need advice onwaht to do? or where i can buy the parts from to get it installed cheaper..|||The Exhaust Gas Recirculation (EGR) valve may have carbon buildup which can be cleaned out without replacing the expensive EGR valve. The adjacent intake manifold EGR passageways need to be cleaned of excessive carbon buildup when the EGR valve is removed. That may correct the engine knock, so do that first.