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IAC Problem, Not IAC Problem which is it???

H

hirvelam

New member
I have a 2008 new to me boat with with a Merc 5.0L MPI with Alpha 1 Gen 2 outdrive with only (61 hours when purchased) 72 hours on it that I purchased last year. The boat ran great all year with issues but I decided to have a bunch of work done on the boat this winter as "preventive" maintenance and for my peace of mind to bring the boat up to my standards. Here is a list of work that was done:

Gimbal Bearing replaced
All bellows replaced
Trim sender/limiter switches replaced
All Spark plugs replaced
tune up done
IAC & Filter replaced
upper and lower shift cables replaced
Water pump replaced

I took the boat out for the first time and had a number of issues that were not problems when the boat was put away. The main problem is typical of what an IAC problem looks like. The boat won't start when cold in Neutral and has to have the throttle advanced in order to start. Once the engine is at operating temperature it is fine. This is presenting as a classic IAC failure but the unit is brand new? I had the mechanic come out on the water and hooked his computer up to the engine and he is unable to override the opening of the valve with the computer. He then replaced the IAC with a second time with a second OEM IAC and the same problem occurred. As we were running the boat he noticed that the IAC got really hot...Unable to touch it hot.

Has anyone experienced anything like this? What are the chances that 2 OEM IAC valves out of the packaging would be bad?

Mechanic said that the IAC isn't throwing an error code, no beeps/tone and no error messages on the digital display on the dash. When the motor was running mechanic pulled the plug on the IAC and immediately got an error code on the computer he had plugged in and an audible signal from the dash.

Mechanic is thinking the ECM might be bad, but with it throwing error codes up it seems like the ECM is sensing things properly. Also the fact that the IAC got so hot it seems like it is trying to open/close/move but unable to which is why heat is building up. Also once running the boat is not idling smooth. it is almost surging (revving up and down maybe a 500-800 RPM surge. This was also a new issue

I am looking for any suggestions on where to start to remedy this issue. Wondering if it is a combination of things that are occurring between the shift cables being out of adjustment and the IAC. Thoughts....????
 
Try putting in the original iac you took out especially since you didn't have an issue with it? to see what happens.
 
Thanks Boat_tech, that is the next step. Although the mechanics notes say he replaced it over the winter because he "Found" it to be bad.... The old was the original for the boat (2008) but again low hours. I have seen these fail at different hours across the board. Don't know if it age or use that causes these to fail
 
In your list of updates in your original post you list "IAC and filter". What filter? I'm wondering if you meant to say IAC muffler?
 
I have the 2002 version of this same engine. The problems you describe above are exactly what I experienced when my IAC muffler (a $2 piece of white fiber/foam located in the throttle body) became very dirty. I've learned to keep my flame arrestor and IAC muffler clean. Once done my problems went away.
 
Struggling to understand how the IAC has anything to do with starting when cold. Is it stuck open rendering your mixture extremely lean?
 
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Mark S. said:
In your list of updates in your original post you list "IAC and filter". What filter? I'm wondering if you meant to say IAC muffler?
Click to expand...

IAC muffler...correct, I have heard of it called a muffler or filter. Since it is pulling air through it, I think many think of it as a filter, even though it does "muffle" the sound compared to when it is removed. [h=1]Mercury-Mercruiser 35-863829 IAC Intake Air Control Muffler[/h]
Either way it was replaced as part of the winter service. during the problem solving period we removed it and put it back in to trouble shoot and it was a brand new piece.
 
hirvelam said:
Thanks Boat_tech, that is the next step. Although the mechanics notes say he replaced it over the winter because he "Found" it to be bad.... The old was the original for the boat (2008) but again low hours. I have seen these fail at different hours across the board. Don't know if it age or use that causes these to fail
Click to expand...

The IAC is powered all the time and grounded with pulses to activate it..... I am also leaning towards you ECM being the culprit. I have seen an IAC with the plug melted on it from a bad ECM.... I am sure there is more damage to other engine functions caused by this... Find a loaner known good ECM.. The ECM does not have to be for a 5.0 to test. any 555 ecm will work Alpha or Bravo, 5.0 to 383.... Just do not drive the boat....
 
Chris,
Thanks for the suggestion. The boat is not being driven nor will it be until it is fixed. Will look into an ECM "Loaner" and see what we can find. Not real happy about having to drop 2k For a new ECM, but if its about the money, then I guess I shouldn't own the boat. In using the loaner ECM, is there any chance something that caused mine to fry could also fry the loaner? Said another way...is something else causing the issue that needs to be addressed first?
 
hirvelam said:
Chris,
Thanks for the suggestion. The boat is not being driven nor will it be until it is fixed. Will look into an ECM "Loaner" and see what we can find. Not real happy about having to drop 2k For a new ECM, but if its about the money, then I guess I shouldn't own the boat. In using the loaner ECM, is there any chance something that caused mine to fry could also fry the loaner? Said another way...is something else causing the issue that needs to be addressed first?
Click to expand...

Where are you located?
 
There are several outfits that advertise on the www that provide ECU diagnosis and repair....another option to consider....
 
Sooooo, i know everyone is curious about what this little gremlin is all about....I got a call from the mechanic that worked on the boat over the winter and has been doing the trouble shooting. It was a really simple fix....He called me (very sheepishly and apologetic) and admitted that he put the IAC on backwards. He had shifted the unit 180 degrees. So everything that was pointing to Vacuum leaks and IAC failure was correct. He threw another new IAC on the boat, tested it and everything ran great. I picked the boat up and ran it myself and everything was running as good or better then before the work was done. I appreciate all the feedback from you guys on the forum. Gave me plenty to research and think about ...I guess I may be looking for a new mechanic....
 
hirvelam said:
Sooooo, i know everyone is curious about what this little gremlin is all about....I got a call from the mechanic that worked on the boat over the winter and has been doing the trouble shooting. It was a really simple fix....He called me (very sheepishly and apologetic) and admitted that he put the IAC on backwards. He had shifted the unit 180 degrees. So everything that was pointing to Vacuum leaks and IAC failure was correct. He threw another new IAC on the boat, tested it and everything ran great. I picked the boat up and ran it myself and everything was running as good or better then before the work was done. I appreciate all the feedback from you guys on the forum. Gave me plenty to research and think about ...I guess I may be looking for a new mechanic....
Click to expand...


This makes perfect sense... The air flowing through the IAC in the wrong direction will load the motor and over heat it.
 
SO out of curiosity, what way does the IAC go? I have a 2007 5.0 MPI with the IAC mounted directly to the throttle body, not on the intake with tubes running to the throttle body. My IAC is mounted with the solenoid/connector towards the front of the engine. On the ones that mount to the intake with tubes, it uses the same IAC however, following the route of the tubes, mine would be installed backwards. I am having the same issue with my boat stalling after coming off plane and throttling down. Any other time it runs fine but has recently started stalling after starting unless I give it a little throttle. Other than that the boat runs fine. This is a brand new Automotive IAC that has the spring and rod in the top portion of the air ports. When I throttle down, I can hear a louder than normal sucking sound as if the engine is starving for air. Does the MAP sensor have any control or work with the IAC function?
 
rsmith0801 said:
SO out of curiosity, what way does the IAC go? I have a 2007 5.0 MPI with the IAC mounted directly to the throttle body, not on the intake with tubes running to the throttle body. My IAC is mounted with the solenoid/connector towards the front of the engine. On the ones that mount to the intake with tubes, it uses the same IAC however, following the route of the tubes, mine would be installed backwards. I am having the same issue with my boat stalling after coming off plane and throttling down. Any other time it runs fine but has recently started stalling after starting unless I give it a little throttle. Other than that the boat runs fine. This is a brand new Automotive IAC that has the spring and rod in the top portion of the air ports. When I throttle down, I can hear a louder than normal sucking sound as if the engine is starving for air. Does the MAP sensor have any control or work with the IAC function?
Click to expand...
Automotive IAC will not work.
 
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