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  1. #1
    Join Date
    Jan 2007
    Location
    Washington, DC
    Boat
    Sea Ray
    Details
    300 Sundancer 2002
    Engine(s)
    5.0 MPI, Bravo III Drives
    Posts
    58

    Merc 5.0 MPI - Idle Air Control Valve (IAC)

    All,

    Just had a failure this weekend on my IAC (controls engine idle speed/start up air mixture). This part is about $90 and is very easily replaced in 2 minutes. The reason I'm posting this is that I feel you should have one of these, and the gasket that goes with it (doesn't come with the IAC), onboard, because if it goes, you're dead in the water.

    Symptom was that we were steaming for about 1 1/2 hours on the bay and then slowed down to idle in the Baltimore Harbor. At that point, the starboard engine died. It wouldn't start after that. The engine would crank, but not start.

    If you have Smartcraft installed, it will tell you exactly what's wrong. I don't have Smartcraft in my boat, so a tech from Clark's Landing Sea Ray came to Baltimore and hooked his computer to my engine, read the code, and replaced the IAC and gasket in 2 minutes. He said it's a common failure. So, I ordered an extra IAC and gasket just in case the port engine decides to do the same thing in the near future. The IAC sits on top of the engine, right after the flame arrestor. It's held in place by 2 hex bolts, and requires a new gasket that's sold separately when it's replaced. I've added a link to the schematic for the throttle body which shows the IAC and gasket (parts 15 and 16).

    http://www.marinepartsexpress.com/Merc_Schematics/5.0L%20MPI%20ALPHA-BRAVO/0M300000_0M599999%20(USA)/THROTTLE%20BODY.pdf

    Happy boating!!
    Eddie

  2. #2
    Join Date
    Oct 2006
    Location
    Wisconsin - Winnebago Pool chain of lakes
    Boat
    Sea Ray
    Details
    280 Sundancer, Westerbeke MPV generator
    Engine(s)
    twin 5.0's w/BIII drives
    Posts
    4,504
    In a pinch you can go manual and not use the IAC control valve to get home.

    Disengage your drive. On my 280 Sundancer this is done at the helm by pressing a round black button at the base of the throttle that controls the engine with the issue.

    Next, move the throttle forward about 1/3rd of the way.

    Now, start the engine as normal with one hand on that throttle. Be ready to add more throttle or less based on the engine revs. Settle in at about 1,200 to 1,400 RPM’s.

    If you have twins like me, get moving forward with one engine. Obviously skip this if you have a single engine.

    Now, add some more throttle to the effected engine. Get her to about 1,600-1,800 RPM’s then quickly pull back on the throttle and as soon as you are back in neutral your drive will reengage then push the throttle forward again, getting her back up over 1,200 RPM’s. This back and forward movement is all one motion taking less then 1/2 a second. Do it to slow and the engine will shut down. If that happens, start over.

    This is hard on your drive however it’s not that hard on it and you can now boat back to your marina. If you have two engines you should come into your slip with just the one that is working. The above technique makes you take off with a bit of a jerk so if you only have one engine you may want to row into your slip with a paddle, water ski, wakeboard or what ever you have available.



    Note: If you go the route of keeping a spare IAC control valve onboard (I don’t see why you would keep a spare gasket) make sure you have the proper size allen wrench (hex key) to change it. It’s a odd size that is not one of the sizes in many of the small fold out allen wrench kits. I do keep a spare IAC onboard plus the correct size allen wrench.
    2003 280 Sundancer twin 5.0 BIII
    Westerbeke MPV Gen added Feb '08
    Presentation

    Where we're going we don't need roads-Emmit Brown a.k.a Doc

  3. #3
    Join Date
    Oct 2006
    Location
    Upstate South Carolina
    Boat
    Sea Ray
    Details
    2006 260DA
    Engine(s)
    350 MAG Bravo III
    Posts
    5,971
    I keep a spare on board for this same reason. I have had them fail before and it's no fun when that happens.
    2006 260DA............Former Sea Rays..... 1999 210SD ...... 2002 240SD

  4. #4
    Join Date
    Jan 2007
    Location
    Washington, DC
    Boat
    Sea Ray
    Details
    300 Sundancer 2002
    Engine(s)
    5.0 MPI, Bravo III Drives
    Posts
    58
    Wow! Thanks much! Very cool that you can work around it. I wonder why the Sea Ray tech didn't tell me to do that? Oh, that's right, it would have been free that way... I think folks with Mercs should be aware of this technique though. It's a life saver.

    Cost was $420 for holiday weekend dock service... However, we were up and running. So, I guess I can't complain too much.

    Eddie
    [/img]

  5. #5
    Join Date
    Oct 2006
    Location
    Tacoma, WA
    Boat
    Sea Ray
    Details
    290 Sundancer
    Engine(s)
    Twin 5.0L EFI Bravo
    Posts
    106
    Great tip!

    Tacoma 290
    2000 290, T-5.0 MPI

  6. #6
    Join Date
    Oct 2006
    Location
    Wisconsin - Winnebago Pool chain of lakes
    Boat
    Sea Ray
    Details
    280 Sundancer, Westerbeke MPV generator
    Engine(s)
    twin 5.0's w/BIII drives
    Posts
    4,504
    Quote Originally Posted by Water U Lookin' At
    Wow! Thanks much! Very cool that you can work around it. I wonder why the Sea Ray tech didn't tell me to do that? Oh, that's right, it would have been free that way... I think folks with Mercs should be aware of this technique though. It's a life saver.

    Cost was $420 for holiday weekend dock service... However, we were up and running. So, I guess I can't complain too much.

    Eddie
    Glad to help.

    There are just so many things to know. That is what makes this CSR forum so great. I have learned a great deal and am happy to help when I can.
    2003 280 Sundancer twin 5.0 BIII
    Westerbeke MPV Gen added Feb '08
    Presentation

    Where we're going we don't need roads-Emmit Brown a.k.a Doc

  7. #7
    Join Date
    Oct 2006
    Location
    Somers Point, NJ
    Boat
    Sea Ray
    Details
    "On Vacation" 2006 40 Sundancer E120 Radar & Garmin 5208
    Engine(s)
    QSB5.9 380 Cummins
    Posts
    1,396
    I also keep one of these in my spare parts bin (actually my bin is the white one Kohler includes in theire genset tune-up kit).

    On fuel injected vehicles, engine idle speed is controlled by the Idle Air Control motor. Commanded by the ECM, the IAC maintains idle speed by varying the size of an air channel that bypasses the engine's throttle plate. By allowing additional air into the intake manifold, the IAC compensates for engine temperature and load variations. The IAC motor retracts and extends in small increments commonly referred to as counts. A count of 255 indicates maximum bypass and full IAC retraction, whereas a count of 0 indicates no bypass and full IAC extension.

    If you are having problems with idle controller (won't stay in idle) and DO NOT have an IAC spare, here's another tip in an emergency.First let the engine cool and remove your IAC. You will see a small black flange which will likely be stiff and difficult to move. Give it a SMALL dab of WD40 or other silicone lub and then move it gently with your finger. Replace the IAC. This will get you home (with or without the gasket) but you should replace the unit and gasket asap.
    Previous Boats
    2004 280 Sundancer, T 5.0/BIII
    1998 21' Bayliner Capri

  8. #8
    Join Date
    Feb 2007
    Location
    chesapeake
    Boat
    sea ray
    Details
    36
    Engine(s)
    cummins
    Posts
    307
    Just replaced an IAC valve as well. Had it go bad...but used more throttle at idle until I got back home from a week long trip. Once home got the valve and installed it. $97 for the valve and gasket, easy work.

  9. #9
    Join Date
    Feb 2007
    Location
    New York City
    Boat
    Sea Ray
    Details
    1996 450DA, TNT, Caribe dink w/15hp OB.
    Engine(s)
    3126 427HP TD transmissions
    Posts
    7,319
    Damn, I wish I could find the website I bought mine from. $72 took two weeks to get here but it was a spare so...

  10. #10
    Join Date
    Apr 2007
    Location
    NJ Shore
    Boat
    Sea Ray
    Details
    SeaRay SunSport
    Engine(s)
    5.7LX
    Posts
    4,216
    I am having a blond moment

    I am 90%+ sure my 1997 5.7LX engines are not fuel injected. They don't say EFI on them, and they sure take a fair bit of cranking for the first start of the weekend.

    In this case (after looking at the schematics), I don't have an IAC valve to worry about, correct?

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