I know this issue has a lot of threads on it and i have read most if not all of them.
Here's the issue i have a 575sci it has about 50hrs on it from the last complete rebuild, After a timing issue and a bad cap the thing runs strong. But resonantly when i would put it in neutral the RPM will jump up to 1000/1100 and then slowly settle back down. For me this makes it hard to park and hate that i have to sit and wait for it so can put in gear.
I replaced the TPS and the ICA motor and still no luck, i have no scanner to check the volts or the ica count. i took it in to have the shop hook it up and give me some info. They called me back and said "we called mercury racing and they said this a known issue with a single ICA motor so we need to send the ECM in and have them reprogram it for 2 ICA's and the we may need to buy a new wiring harness to handle 2 ICA's or rewire the motor. and then said that other than that we will could try to trouble shot it @$110 an hour.
I asked what the ICA count was and he said that it didn’t matter because the ECM controls it and you cannot adjust it.
So i ask Steve Zuckerman (OSO member) and he gave me a few things to try and i will when i get it back today.
Has anyone out there fixed the issue and if so how?, without buying a different blower, new ignition system or reprograming the ECM?
Mike

Mine would occasionally idle weird ( both of them at times)

I overhauled the engines, did some mod's thus had
to have the ECM's modified, they no longer do any of that
goofy sh!t.

Dean Gellner did mine.

A friend of mine has a pair that are dual IAC's,
he's experienced an occasional idle problem too.

I have had the initial high idle at startup but never when going back to neutral. Sounds like a blade is sticking open.
Use a feeler guage on the back throttle body to measure the blade opening. I know there is a spec on it somewhere and to adjust that you need to drill out a plug.

Maybe the back blades are open too far and front iac is struggling to bring the idle down. Or vacuum leak?

My whippled hp500efi occasionaly does the same thing. Efi engines are programed to burn excess fuel in the intake track before resting at idle. If it lasts more than a couple of seconds you prob. have a problem. Got to get it scanned to know for sure otherwise its a crap shoot. Why did your mechanic call mercury?He should have scanned it, sounds like he does not have one or he would have scanned it. I would find a mechanic that is not relying on what merc. says,rather what the scanner says.

Thanks and keep them coming i am heading out to get the boat now. they do have a scanner and he will send me the printout. remember i have just one ICA on mine.
I am not sure why he called them stumped?
I saw a thread about setting the gap and i will look in to it.
Also there was a service bulletin on how to fix this issue by adjusting the throttle plates.....somewhere?
thanks all for the info

Check your timing,if its not dead on it will blower surge,,pcm relies on the correct timing for the distributor's reluctor wheel to inject the correct amount of fuel at the rite time..

thanks everyone this gives me some starting points.

here is a good link put in your year and find services bulletins
http://www.ishopmarine.com/ishop/jsp...smBcatList.jsp