Reckless wins the prize....I was just going to update this thread and thank everyone for their time when I saw your post. Service pulled the codes again and this time narrowed the investigation. Trying to manipulate the IAC by raising or lowering the idle through the computer interface revealed a definitive problem there. Removing the old one it was visually apparent it was damaged from heat. With the new on installed ($150.00 retail), the boat idled smoothly and sounded healthy. Back on the water I felt the difference right away, the boat felt lighter. A quick romp across the lake and it was apparent the problem was fixed as I actually picked up the original 6 MPH I lost from last year and added another 1-2.

This makes me wonder how long that plug wire was off the #8 cylinder? I mean, a couple of years ago it felt like a lost a mile or two...right around the time I replaced all the plugs. I never really thought to much about it and attributed it to weather, load, age of the motors, trim setting, etc. Maybe I never really had the boot over the plug body properly as the #8 starboard plug in a cat is a huge pain to get to.

Thanks again!

Very cool, glad you got it nailed down. Funny thing the IAC electrical plug on my port engine began smoking last time out meaning IAC is toast. Soooo just to make a quick run out to the local beach for a few hours I simply unplugged it to stop the annoying alarm and continued on with my day. I will replace both and keep the good one on the starboard side handy as an emergency spare.

Thumb's up to NK for following up with results.. Too many people on here asking for help and not posting results.

Chris

Don't know about you, but my spare parts bin on the boat is getting a little crowded the older the boat gets

Building my spare parts list for my twin 496ho 2 xIAC 2x belts spare boost pump and set of plugs ,found a fairly cheap place for the iac $106 each belts $58 each . Still havent solved my intermitent fault , having to run boat up and down close to boat ramp with fuel presure gauge conected , been out twice and it ran perfect ,going out for longer next week and see wot happens, my post from about 2 weeks ago explains wots goiing wrong with the starboard motor.