Marrs, Welcome to FIP/warm idle/fuel management, MB style. With the engine warmed up to operating temp, 1)idle at 750 rpm (with 50 rpm of rich), 2)WRD air shut off, 3)WRD heat element has extended to move the FIP WRD/barometer lever to max(no fuel enrichment), 4)CSV closed, 5)venturi butterfly closed. This means the FIP is pumping just enough gas to run the engine at 800 rpm with optimum idle air at elevation. Closing the idle air screw will decrease rpm(close idle air a little to get 750 rpm). Opening the idle air screw will increase rpm to 800 then further opening will decrease rpm.
ah ha, FIP nirvana!