My starboard engine started throwing "Engine Fault - IAC Output" yesterday (Mercury Racing 600SCI motors). We let the motors cool down and I made sure all the electrical connections were good to the Idle Air Valve and re-seated them. Started the motors back up and the starboard it immediately threw the same error code. We limped home on the port motor.

Before i started ordering parts and working on it i wanted to ask a couple questions since there is alot of knowledge from everyone on here.

1. I'm assuming this error is referring to the Idle Air Valve...correct? http://www.boats.net/parts/detail/merc/M-862998.html
2. I plan on replacing the Idle Air Valve.......Is there anything else i should check with this fault?
3. What is the best way with a multimeter to test the old Idle Air Valve after removal to see if it is in fact bad?
4. Where do yaw buy your Mercury Racing Parts?

Thanks for you help in advance!
Southernhick

It's a common problem on the 600SCi & 700SCi. If you check the IAC with an Ohm meter and you will likely find that is it shorted with 0 Ohms. You can buy an exact replacement at any auto parts store, the AC Delco part is #AC423. The bad news is that these failures often cause damage to the PCM which means you might still have the IAC fault even after replacing it. Dustin Whipple can usually repair the PCM or you will need to order a new one from Mercury Racing. Whatever you do do not swap the IACs between engines to troubleshoot the issue as you will also damage the other PCM.

Installing a 1 amp inline fuse on the positive side of the IAC will prevent another IAC failure from damaging the PCM.

Good luck,
GF?

had a friend with screwy issue on same engine, turned out to be a issue with the wiring harness....very $$$$$$

Yes....the bad IAC shorted a chip on my PCM. Sent my PCM to Whipple and they fixed it! Thanks for your help.

Glad it worked for you. Make sure you install a fuse to prevent it from happening again.

GF?

What size fuse? I was told to put a 5A fuse in, but that seems very high. I would think a 1A fuse would be adequate.

1 amp is what I've been using and it works perfectly. A 5 amp fuse will not protect the PCM.

GF?

Thanks.

I believe I saw your boat at PBC when we were shopping?? If that is yours, it's in really nice shape!

Yep, that's my boat. Always stored in a heated warehouse and never been in salt water. It's still for sale if you know of anyone looking.

GF?

Is there a way to tell if the PCM is damaged by a bad IAC?