Merc 5.0 MPI - Idle Air Control Valve (IAC)

[Water U Lookin' At]

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

 

[Presentation]

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.

 

[Dave S]

I keep a spare on board for this same reason. I have had them fail before and it's no fun when that happens. :thumbsup:

 

[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
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[Tacoma290]

Great tip!

 

[Presentation]

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.

 

[gerryb]

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.

 

[Overextended]

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.

 

[Turtlesboat]

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...

 

[comsnark]

:smt101 I am having a blond moment :smt101

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?

 

[Dave S]

:smt101 I am having a blond moment :smt101

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?

I think they made both a Carbureted and an EFI version of the 5.7 in 1997. If it's EFI, it will still have an IAC but it is a different design than the ones on the MPI sytems we are talking about here. On the EFI system you have what looks like a carburetor (it's official name is Throttle Body) and there are usually two injectors in the air intake opening. The IAC itself is bolted to the side of the throttle body. When you remove your flame arrestor it will be pretty obvious if you have a Carb or a Throttle Body.

 

[NautyDog]

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.

As a general rule, you should always change a gasket when changing an item that uses a gasket. The reason is that a used gasket is worn in the position of the old part and it's orientation. A new gasket will form a better seal, and the original gasket has a higher chance .

Some say that if you re-assemble with the original part, then you can use the original gasket if installed in the exact same orientation, but others would not agree.

 

[Presentation]

IAC filer?

I have one engine that is a bit louder but not a lot louder, it’s more like a high pitched whistling noise.

Another person told me I need to buy an IAC filter.

I have confirmed that this part does exist, its Merc part 8M2001030. It’s not expensive.

It’s not obvious to me where this filter would go.

I did find this online tool. Its a drawing to show where this filter goes.

http://www.marinepartsplus.com/catalog/mercruiser/serial/350+MAG+MPI+MIE/884718003/12841-60

In the drawing, its part #12. You mouse over the area to blow it up so you can see it better.

 

[jg300da]

Yup, had that same symtom once, no idea where the old filter went but one day the engine was quiet and the next day I had this whistling noise. No need to by the part from Mercury, any piece of approx 1" x 2" poly filter media or equivilent will work. As for the location, just remove both spark arrestors and compare the quiet engine and you'll see where it goes.

 

[Calm Crews]

I know this is an old post but, I have 8.1’s also. My IAC alarm is going off so I replaced the IAC. I put a new one on and the alarm never turned off even after resetting. So I swapped it with the side I know works and still the same. The motor is running fine doesn’t stall anymore. Anyone have an idea on what to do next to get the alarm to go away?