Engine chatter at idle when light load on port 8.1 engine

[2003380]

When I'm at idle on the port engine (650 rpm) and have starboard engine slightly higher (800 rpm) the port engine chatters as if it is misfiring. This only happens when the port tranny is engaged and stops if I put the port tranny in neutral or increase rpms.
Mechanic changed a computer idle module and no change. Runs fine otherwise.

Mechanic says leave it alone.

Plugs, wires, coil?? What do y'all think

Thanks

2003 380 sundancers 8.1 gas

 

[bluebelly]

are you sure the noise is not coming from the transmission bell housing? That is where the flex plate is and it could be that.

 

[2003380]

Engine jumping around like a mexican jumping bean as if misfiring

 

[NorCal Boater]

Sounds to me like the idle is too low. Can it be adjusted?

 

[Turtlesboat]

I had the same kind of thing happen to me last year. The drive is not fully in gear at idle. If you pull or push the shifter a little more, and then back to idle, it would lock into gear. I adjusted the shifter cable and it locked into gear correctly. try overshooting the idle point and then click it back to see if the problem goes away. Might be the same thing as me.