Yeah , I am also curious about the IAC .... here's what I am thinking ... if the engine drops significant rpm's because of IAC being stubborn maybe the buzzer is a result of a low oil pressure ? Like Chaoscube said it solid but short ...

I've been there before...save yourself a lot of time and effort and get it scanned. You'll be chasing things forever if you don't.

It sounds like there are multiple things. When was the last time plugs and wires were changed?

Water pressure sensor are a common problem for going bad. just an FYI

IAC longevity - when replacing to new - use a quality IAC sensor to begin with. I know a lot shop online and as always you get what you pay for. China stuff all over the place for marine parts,

Next is to clean mounting surface - install new gasket - install using properly torque specs for new IAC and do not crank down all in one pass.

things that shorten life of IAC

Dirty flame arrestor and or restricted flame arrestor -
dirty or ingested IAC muffler
dirty IAC muffler cavity
restricted passages and or hose connection to IAC
Improper belt tension and or off alignment of belt(s) creating belt dust
Belt dust and passing thru flame arrestor
rusted pulleys creating belt dust
Did I say belt dust huge killer of an IAC for these engines
Leaking hose connection
heat related
deposit build up pintle

And of course IAC failure can still take place even in a perfect world.

Boost pump, I have 3 psi
Check valve on the engine fuel rail ,I have 43 psi and when engine dies, I have 35-38 approx

I have removed the flame arestor for all the test I did

I have openen and tested the IAC...resistance and voltage is also good.

Going to drop the boat to the damn dealer tomorrow morning. I hope they will not take 2 weeks to scan the boat.. I will keep you posted guys and thanks for your help

Yep, that one got me recently...same with water temp sensor.

I don't think either of those would cause his symptoms but certainly could be the alarm problem.

Bravo app you should have gen 3 cool fuel - inside the that cool fuel and only that cool fuel set up is a 10 micron disc pad fuel filter - it is dead bottom inside the cell - they clog very easy and need to be changed once per year bare min, then you have the paper element fuel filter located in the basket pull out - the basket pull out is your water separator - it will collect water and needs to be dumped and check every so often. the fuel filter that's sits in the basket needs to be changed out bare min once per year as well.

I always change them at the beginning of the year but check all of it during winterization. Maintenance is the upmost importance of this cool fuel. 99 % of boaters never do it. hence fuel pump problems.

next is the internals of the gen 3 cool fuel has black paint - guess what peels off and runs thru then clogs the whole fuel system including the fuel pumps ? THE BLACK PAINT.

Your 383 in not the standard PRODUCTION Mercruiser engine. Yes it is a Mercruiser but comes from the reman side as drop in. I have seen them use Gen II as well as the GEN III cool fuel apps. Just giving you heads up about the GEN III because they do not have the spin on fuel water sep filter - everything is internal for the GEN III cool fuel including the fuel pumps - good luck

Also it is the upmost importance to drain the GEN III cool system itself during winterization. I have 3 here in TX that were not drained and all 3 leak water and one leaks gas and water - all at the cool fuel assembly. The rest of the boat and engines were properly winterized but they missed the cool fuel. FYI and again good luck

One last thing in addition to all the good advice here. Check your cap and rotor, they get corroded and just plain wore out. That could easily cause this.

I have GenII cool fuel system.
I changed the cap/rotor/spark plug wires 2 weeks ago before starting the engine. I check again this weekend to be sure everything is good and yes it is.
Waiting for news from the dealer for the Scan