I have a pair of 2003 6.2 with ECM 555. Diacom software showed IAC at 99.9%. And didn't respond to the IAC test via the Diacom. No change in idle at all. Boat has been at 90% Guardian. Installed a new IAC, showed 99.9% also. IAC motor was hot. All this at 150 degrees engine temp. Seem 160 engine temp the IAC continually decreased to 0%, stayed there and shows no rpm change via IAC test.
Also unbolted IAC, performed IAC test, seen no pintle movement.
Any good way to test if my driver in ECM is Burnt out?

Hopefully BUP will respond to your post.

First do not use an aftermarket IAC and do not use the auto gaskets that some people sell and or pull out of the box, I can not tell you how many people I have told including some businesses about selling the auto IAC gasket that had no idea. Thats why its always good to follow people that really know whats going on. . Next is the connector can be bad from heat or moisture. There is many important things about the IAC system as in the industry it can be called IAC maintenance.

With all that said ---- Actually not watching your scan on this to give out 100 percent related whats really good or bad. or ugly with the engine along with the ecm. I will tell you this from repairs almost everyday. The 555 s are one of the weakest internal in the marine market. All ecms can live longer and better in a perfect world. Meaning they hate vibration - moisture, improper voltage - voltage spikes ans so on just as other branded ecms / pcms/ do. With that said the 555 experience more internal; failures than MEFI s ever did and way more failures than E controls inwhich everyone is using except Merc... E controls is used by Volvo - Indmar - PCM, Crusader - Ilmor and MEFI 7 currently is used by Kodiak and marine power.

For cat emission control ( EC) engines Merc does not used the 555 anymore. Thank goodness.

The scan tool is your best bet to figure out the IAC for a boat owner - a fully warmed engine thru out all rpms should be monitored. And reported if all possible unless the engine will not allow any of that. Then of course one has a problem. The IAC driver / H bridge fails pretty easily on the 555 s but most of it is owner operator error and mostly lack of ontime PROPER maintenance that cause about 85 percent of marine ecm / pcm failures.

The Merc IAC It is a really bad design to say the least. Regardless Volvo never has this kind of failure and I work on alot of volvos as well. Many 496s and small blocks EFI & MPI engines.. Very possible your IAC internal circuit / driver is bad. If one keeps on running the engine, one can make matters worse and way more expensive. Bench testing can determine all the good bad and ugly for your ECM 555 or for any ecm.

Multiple testing tools are used.. First and foremost is a battery / power supply. Next is -- testing with a Scope and know alot about wave forms. Can you open up your pcm and adapt correct power and controls to operate & monitor all parameters and change the values to see what is operating in the correct spec ranges and so forth ?

And course alot of ecm s and pcm s are fixable as well. Been down this road many of many times seeing all of it when opening up the ecms / pcms

BUP, got my IAC issue fixed with the correct IAC. Mine was replaced by one of it's former owners which had a spring on the valve rod/shaft. correct IAC doesn't have the spring. Post photo of old IAC?

I'm only finding part number 862998 looking thru BAM for every serial number run on base model and also looked at several HO's all the same

Have replaced one my self (6.2) and watched two others replaced (6.2 and 496 HO) and all had the spring, old ones did not have spring and none have shown any issues. All where Merc OEM parts

https://www.mercruiserparts.com/496-mag-base-model

Thanks for reporting and glad all that was fixed up correctly after I sent you the correct parts. Actually by your scan report that 2 things were possible taking place there. And I was 1600 miles away haha.

ANYWAYS the aftermarket IACs cause more issues than they are worth - yes I know the aftermarket IAC s only cost 60 to 90 bucks total --- man what savings of about 30 bucks because I know that the OEM IAC's really is needed plus the real required gasket. The gasket is very important as well.

If one wants the real info and the correct info what to do about anything IAC related because I know all of it - hit me up .