I am having issues with my 2004 496ho. It started idling rough, almost like I had bad fuel. Once you accelerated, it cleaned up and was fine. Changed the fuel/water separator and drained fuel and added new. No change, in fact it was worse. Still idled rough, but now it wouldn't even plane. Acted as if it was loading up on fuel. Pulled the codes and got cam position sensor, crank position sensor and MAP sensor. Mechanic replaced MAP sensor, cleared codes and boat ran fine...once. Next time out, same issues. I don't know what codes the ECM is showing, and I am not getting any beeps. I'm pretty sure it's not the MAP sensor. Any ideas what the issue may be?

was to change the plugs. Voila!

+1

Could be the idle air control valve.

An the IAC valve are My thoughts. Do the plugs for sure. I read alot of people that had problems with the plugs. Artie

Crank sensor gets my vote. Just replaced both of mine.

That's what I am leaning towards as well. How bad was it to replace?

Don't change the crank sensor yet. Those were not much of an issue in 2004 unless your engine is a 2001-2003 actual engine model year (check tag date on heat exchanger) If your plugs are original and unchanged give that a try first, also check and clean the IAC filter piece inside the throttle body if its still there. If that little filter has broken up and been sucked into the IAC itself it can cuase a condition like this. Unbolt the IAC on the back of the intake manifrold and clean it with carb cleaner and look at the plug on it and make sure its not starting to melt and distort.

Best Regards,
Ray @ Raylar

Mine are 2002. The sensor that was acting up was a little tight to pry out, the other one slid right out. Be carefull not to bend them sideways, they are not hard to break, but they ARE hard to get out once broken. Be sure to use penetrating oil, and the new ones shouldn't have the lower o ring, just the upper. Follow Rays advice first, he knows best. Good luck, keep us posted.

Ray,
Would it have thrown the ckp code if the iac was the issue? These ecm's do seem to like to store a lot of codes.