whatever this is, the engine behaviour seems odd to me, i hown and fly with all the warbird in DCS , on the corsair (i love it !) what i do is i'm always full throttle ahead and only move the governer command, it seems to stay in the good value for manifold and RPM which is strange, if someone can try this too.
Also the mixture is important and must be set accordingly to condition, middle position for landing, take of and transit, and full ahead when you need power, for combat.