SO can one of you help me understand what determines desired idle speed using a rinda pro ? I noticed on one of my 502 mag mpi motors that the iac had died and was no longer controlling high idle at startup as I could not hear any sucking noise on the port motor. I ordered a new iac and cleaned the tube it mounts in and engines runs fine, new iac works but I cant get the motor to idle down below about 830 to 850. I have tried tuning the secondary screw and the iac does try to compensate for adjustment. My concern is that the desired idle speed per the tm pro seems to be set at 840 ish and Im not sure how to adjust the desired idle speed.

try turning the primary idle screw,also check that the cable is letting the primary blade to close.

I have made sure that the primary is closed and my scanner shows .03 TPS at idle. Cable disconnected

Isnt the desired idle speed programmed into the ecm and it should not change or does the ecm change it due to other parameters ?

Yes the idle speed is programmed into the ECM. You can’t change the idle speed using the Rinda. You can only observe the “set” speed and “actual” speed. You would need to buy the software to change it or take the boat/ECM to someone who already has it.

only other thing that could change the idle would be the water temp sensor.idle is ecm programmed .
on edit,,just looked at the mefi1 config.,,seems it has some "field service mode desired idle speed" maybe you executed that command some how.