454 mag mpi inboard stalling when put in neutral intermittently
 

I have a 2000 454 mag MPI that I am having issues with stalling intermittently when put into neutral. The IAC and TPS sensor have been changed. I spoke with a mercruiser mechanic today who said the throttle plates could be carbon up causing the issue. When I ran that by the guy I bought the boat off of he told me he just clean them and they were clean. he did tell me though that the throttle plate seem to be slightly open and when he spoke to Mercruiser they could not tell him what the specs were. Does anybody know if the plates are supposed to be fully closed in neutral and is there an adjustment?