I have the same problem with my 260E. I had it checked and the result was, the black electronic box at the side of the airflow meter assembly was faulty.
About your question, what's under the plate? There is a spring attached to the arm connected to the circular thing that opens on top of the assembly for air. When you open it, there's no need to worry cause it's mechanical. The only thing you should worry about is the black box attached to it cause I learned that it is calibrated so tampering with it is a no-no.