Mismatched Engine RPMs

grouch0jrgrouch0jr Member Posts: 181 ✭✭✭
in General Boating Discussions
So I noticed that once my engines are warmed up and idling port sits at about 550 and starboard sits at about 720. I connected the Techmate Scanner and performed the IAC Output Test on both engines. The port engine was responsive to changes to the IAC signal, but the starboard engine was not (-100 to +100 no real change). Does anyone have experience with this test? I've got a spare IAC, it's not much trouble to swap, but don't want to if i don't have to. Could it just be seized, or in need of a cleaning?
2006 342EC - Twin Mercruiser 350 MAG MPI Horizons
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  • davidbrooksdavidbrooks Member Posts: 1,428 ✭✭✭✭
    Look for a vacuum hose that may have gotten disconnected. Also take the flame arrest off and see if the RPM changes if there is a very small filter that is added or removed in the gap in the flame arrestor. I've used a small Brillo pad that I've cut up before to replace it when it goes bad
    It's 5 O'Clock Somewhere!
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  • grouch0jrgrouch0jr Member Posts: 181 ✭✭✭
    I know my IAC filters are good, I just replaced both of them. I'll look for a disconnected vacuum line. Should it be connected to the throttle body?
    2006 342EC - Twin Mercruiser 350 MAG MPI Horizons
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  • grouch0jrgrouch0jr Member Posts: 181 ✭✭✭
    Just to close the loop on this, today I swapped my IAC on the starboard engine and both motors idle dead-nuts-on at 550 now.


    2006 342EC - Twin Mercruiser 350 MAG MPI Horizons
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