I have a 02 37 Formula PC with twin 375hpVolvo 8.1 GI-A duo props. The starboard engine idles at 650 RPM in neutral and about 600 in forward. When I shift into reverse the idle drops to 475-500 and is very rough. The engine sometimes starts in this condition but if I shift in and out of forward the idle goes to 650 but the problem with reverse idle is still there. No other performance issues exist. I am thinking its either the IAC sensor of the TPS sensor but am not sure. Has anyone experienced this problem?