7.4 Liter MPI idle problem
 

I have a 1997 Merc 7.4Liter MPI, it has an intermittent idle problem . Sometimes when at an idle in gear it will spit, sputter and backfire and then stall out. If you go to start it again it is ok. I got a code 33 from the ecm which is for the map sensor, I tested the map sensor and it tests ok, so I have cleared the code and then the idle problem returns along with the code, could the map sensor have an intermittent problem?

Thank you,

Brian