IAC whistle ??? Merc 7.4L MPI

[tpenfield]

Greetings -

The last 2 times I've shown my boat to a prospective buyer, there was a distinct 'whistle' noise coming from the engine(s). (Yes, the boat is for sale) The noise/whistle is while running at idle, engines warm.

I'm thinking it is the IAC, but wanted to check in with the experts before I open the tool box. I *think* the whistle/noise is coming from the starboard engine. It can only be heard with the engine hatch raised and at idle. No issues with normal operation.

Merc experts, tell me about the whistle . . .

 

[kenny nunez]

There is a small piece of foam rubber about 1/2” square that fits in the IAC that muffles the sound. Over time it breaks down. I had that problem with my Donzi and that cured the noise.

 

[alldodge]

Kenny don't think his has the foam piece. His serial number 0F802036 doesn't show one. The flame arrestor item 36 has some filter media between 2 wire meshes.

https://www.mercruiserparts.com/bam/subassembly/31924/2342/14

It does sound like an IAC issue or throttle plate hanging. Might be time for Diacom

 

[Fun Times]

If you haven’t, maybe try cleaning the throttle plates of the body….Both sides…Also I recall you’ve recently readjusted the throttle cables, maybe try aren’t in a proper position creating a whistle while the air moves across the plates…..Also I recall some Merc big blocks EFI’s had a small hole drilled in the throttle plate to help with idle speeds and some didn’t have the hole… if the hole is there, clean it too and check by putting you finger at the hole and all around the plate edges to see if the sounds changes, etc..
Run it with the flame arrestor removed to test as well.

 

[tpenfield]

Thanks guys . . . I am not finding the foam piece in the parts list, so perhaps it is just a cleaning of the air by-pass and throttle plates (which the high speed plate has the hole)

Here is a picture from my recent throttle adjustment work (adjusted port engine only)