Bad idle Fuel gauge not working

[ereed969]

I got my boat out today and my fuel gauge is not working. Does anyone know if it would be just the sending unit or if there is something else that could be bad. The boat should be at 3/4 tank but it doesnt move at all. I also have a bad idle. This was happening last year and I think its the IAC valve. Today i cleaned the throttle body and it hepled but when i unplug the IAC valve the idle doesn't change at all. Does that condirm that the val e is toast. Thx

[boatwakes]

Could you give some more symptoms please? Bad idle doesn;t describe enough. Will it run at idle? Does it stall? Will it accelerate? Can you apply throttle at idle and if so does it run better?
As for the fuel gauge, it's usually the sender that goes bad. Remove the floor of the trunk, that's where the fuel tank is located and then remove the center wire from the sending unit (usually pink) and touch it to the tank, with the ignition key "on", and watch the gauge. If the gauge pegs over full, the sender is bad, if the gauge doesn't move , the gauge is bad.

[ereed969]

Yes when I apply throttle at idle it runs great. I can go high RPMs no problem runs very smooth. Then when just sitting idling it runs very rough then will stall. Thanks for the info on the fuel gauge problem. I will go out this morning to look at that. Thanks for the help I really appreciate it

[boatwakes]

Check the fuel pressure as well, should be 30psi +-2psi but IAC will usually present with hard/no start without slight throttle applied to open throttle plate.

[huntingwiley]

Check the Idle air control. Mercs are known for this. Mine has went bad twice sine I have had the boat and both times had the same symptoms you describe. Its right on top of the engine behind the fire arrestor.