Boat cuts out at idle

My boat shuts down at idle. It does fine at higher rpms, even idles fine after running for a while. When the engine has been off for a while (30-45 min) it does it all over again. I've replaced the IAC valve and the issue is still present. If I put it in neutral and raise the rpms a bit when starting the boat, it does fine. I was thinking maybe replace the MAP sensor next?

kimcrwbr1 said:

Have you cleaned the throttle body around the butterfly good and inside the IAC ports. Somtimes you need to pull it out to clean it properly and use a new gasket when installing it?

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I have not cleaned around the butterfly in the throttle body nor the IAC ports. How would I do that? Specifically the IAC ports. Should I take the IAC valve out and spray throttle body cleaner or something similar? I did take the old IAC valve and cleaned it with throttle body cleaner. When that didn't solve the issue, I then replaced the IAC valve, but still have the issue.

We went out again today and the issue seems to be worse when the boat is in "park" than when it is in neutral. I can give it gas in "neutral" and it revs up fine. However, when I put it in drive from "park" it stutters and dies.