How do i fix my Renault laguna 1.9 diesel?

I recently had a turbo go which i changed ok. shortly after i had a seriuos lack of power even worse on a hill, a local garage plugged it in and told me it was the mass air meter which he informs me he changed, but this did not solve the problem, i have had a mot and the emissons passed ok, does this rule out a blocked CAT from the turbo failure, someone also pointed me towards the agr valve, how can i test this without buying one first, there also seems to be alot of oil in the air line leading to the manifold which ithought was due to the turbo failure and would eventually blow through is this right?