Can either get a Techmate or Diacom software
https://www.rinda.com/marine/marine.htm

The correct info here is depending on the engine serial WHETHER YOU have a IAC muffler or NOT that was designed per Mercruiser set up and calibration. IMO you need a OEM merc dealer who knows the 496 inside and out - Have no idea your location but the 496 is not a stranger to me.

So with that said the first set of 496 engine serial numbers in the 1000s did not USE A IAC MUFFLER and the calibration and IAC PWM was different from the later years and if you or ONE has DTS -- then ONE does not have IAC to even worry about.

You are throwing darts at it and as mentioned from others you possible might have bigger issues going on to worry about.

The IAC just because it sounds like its working means zero - zippo - it is tested / and monitored with a scan tool and calibrated by PWM thru the PCM 555 and if one does not know the parameters per calibrations then one does not know if it is working correctly or not.

There is many things that can cause a IAC to not work properly. One example is Restrictions -- this is a huge issue for it not working correctly. Also buying auto store IAC s is another issue for it not to work correctly.. They do not operate like what Mercruiser used for an IAC and trust me on this one.

Engine serial numbers determine all the part set ups and procedures per engine. Again many 496 s did not use a IAC muffler, as mention here --- depending on the first groups of engine serial number runs and that was for 1000s of 496s. Best of luck with it.