IAC Valve??? - Maxum Boat Owners Club

Lake Murray Maxum · 08-18-2011, 12:17 AM

Hello everyone. Im hoping someone has some ideas.

It has been a summer from h---. From day one of the season, something has gone wrong. I have a 2003 Maxum 2400SC. Merc 350/300 hp w/ Bravo 3. Here we go. This past weekend I took boat out and had a fantastic weekend. She ran great all day! The last time i fired her up she had a lazy start. Didn't fire right up. But she started and we cruised home with no problems. Took her back out Monday evening to enjoy the purple martins at sunset. Couldn't get her started while boat was in neutral. The motor was turning over but just wouldn't fire. Had to rev rpms at around 2k to get started. Once fired up, she sat running at idle with no problem. Cruised back in with no issues. Boat ran great....

Went out today to see if it was just a fluke. NO FLUKE. It fired up. Cut it off. Started right up again. No problem. Third time was not a charm. It would not start in neutral. Same problem as Monday night. Called my mechanic down and he witnessed what was going on. As I revved the rpms to get it started, he saw black smoke come out as the motor caught up to overflow of fuel. He took off my engine cover and looked at the top of the motor. He said that he thinks that it could be the IAC valve. He said that the one on the motor now looks like an original.

In doing some research, I am not sure that this reflects a faulty IAC valve. It currently runs at idle just fine.

I have had lots of things done this season to get the Maxum running like it did last year. Changed the spark plugs, Changed rotary and rotary cap, fuel filter was clean, no water in fuel, put stabilizer in, new battery, serpentine belt replaced. I am at whits end with the boat this year. Its been in the shop as much as its been used for fun with the family. Has anyone experienced problems like this? Could it be the IAC valve (only about a 100.00 fix?)

Any feedback would be very much appreciated. Thank you and I enjoy reading and learning from all the posts.
Mike

CountryME · 08-18-2011, 01:06 AM

I can't speak from boat experience, but I had to replace the Idle Air Control (IAC) valve on my 2001 silverado when it kept kicking an error code. The IAC is a servo motor that runs a rubber stopper against a seat and throttles the air bypass in the throttle body. If the servo motor is going bad, the number rotations that the computer thinks the servo is turning does not match the actual number, thus the amount of air going into the throttle body is not the expected quantity. Since your boat seems to be running rich, this theory seems to hold water.

Check out this site for some non intrusive trouble shooting where you only unhook the electrical plug.
http://www.aa1car.com/library/idle_s...trol_valve.htm

As this site says, it may be a vacuum leak and not the valve. Check over the vacuum lines closely.

Another check you can do is remove the IAC valve and switch the ignition to the on position. The valve should actuate and move outward. Note: DO NOT do this check multiple times, the plunger will run off the threads and the spring will shoot the plunger across your yard or into the water (Ask me how I know this), you will then have to buy a new IAC valve.

My $0.02 Good luck and happy boating.

-JP

Lake Murray Maxum · 08-18-2011, 01:19 AM

Thanks JP! I will check the site out. Hope to get back to the boat on Friday.

ss3964spd · 08-18-2011, 02:33 PM

Could easily be the IAC. Could also be the vacume operated fuel pressure regulator - which, like the IAC, is a common failure point on these engines. Also not an expensive fix.

I believe that if the IAC is having heartburn it will throw a code to the ECM so you could have your mechanic check for codes. If the FPR is acting up I don't think it will throw any codes. Find the FPR, pull the vac line off and see if the inside of the vac line is wet with gas. If it is - bad FPR.

Dan

Lake Murray Maxum · 08-19-2011, 01:04 AM

Thanks Dan. Will check both this weekend.