How can I fix my Renault Trafic 1.9 dci?

My Renault trafic has been standing at a diesel specialist for a number of months now. The vehicle starts, but will not rev up, and remains in limp mode. I have replaced the air flow meter (new from Renault), and had the turbo reconditioned, as well as replaced some vacuum pipes. The EGR valve has also been cleaned, but the problem persists. The technician insists that the airflow meter is faulty, and a new one will rectify the problem. The cost of this part is prohibitive,and I do not want to buy another one. just to be told the problem is still there. Does anyone have a solution to this problem.