Merc 496 HO serging at idle
 

Have a 03 Sonic 31 SS with twin Merc 496 HO's
the stb motor originally had a miss, rough idle.
found on the computer #8 injector was bad.
replace the injector, motor runs good.
Now I'm noticing the serging of the motor thru the air cleaner at idle ? Port motor does not sound like this at idle.
Any ideas what could be causing this ?
Almost sounds like its struggling for air.
Thank you
Bart

I'd try swapping the IAC idle air control valve over from the other engine to see if the surging goes away. There's also little sponge "mufflers" that are supposed to be by the throttle plate behind the air filter that can be missing over time. They help quiet the sucking sound. The are called IAC mufflers.

Awesome 87
Really Appreciate the response
I will definitely try it
Bart

If you plan on keeping those motors, a scan tool would pay for itself. I use Diacom software. If the IAC is bad a scan will easily diagnose. The IAC level should be going up and down.