Rough Running

[joe66]

I have a 2010 Mercury 40 hp 4 stroke 3 cyl. The engine runs smooth in neutral and in reverse. When I shift into forward the engine runs rough and shakes. The engine will run good after it reaches about 1100 RPM. I have replaced the plugs and fuel filter and had the injectors cleaned. The idle speed in neutral is 870 rpm. when in reverse it is 820 rpm. when in forward it is 820 rpm. This has been
going on for a long time. It did not get any better or worse after changing plugs or cleaning injectors.

[boats.net]

Have you checked the prop, does it have damaged blades is the prop shaft bent? If you have another prop put it on to see if makes a difference.

[joe66]

The prop and lower unit are in good shape.

[boats.net]

Probably need to have it put on diagnostic computer and check TPS, ignition and injectors at idle speed. The idle is a little high which could mean there is an active trouble code.