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IAC Part Number for Mercruiser?


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Hi Everyone - we had the IAC go out on one of our engines over the weekend. Does anyone know the part number? It's a 2003 MerCruiser 5.0 MPI. 

Also, I've read conflicting reviews about the OEM part and an automotive equivalent. Thoughts? 

Thanks!

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I just put one on '05 5.0 MPI 2 weeks ago.  Works perfect.  

STANDARD MOTOR PRODUCTS

AC423

Idle Air Control (IAC) Valve

$ 41.79

$ 0.00

This is from Rock Auto.  If you put in the AC423 in has the #'s that this replaces and I believe one of those is actually the mercruiser #.  This particular # doesn't come with the right gasket however, comes with sort of a molded o-ring made to fit in a groove.  Either get the gasket separately from Rock Auto, or you can pick up at any auto parts for next to nothing.  I believe the Mercruiser is north of 100 deer for the IAC. . 

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Ours went out at 320 hours.  Apparently the 300 hour mark is when they go (so get two if both engines are about the same hour mark).  We used the Mercruiser part, but I've also heard conflicting things about OEM vs. automotive equivalent.  Since it's something you can change yourself, I'd go with the OEM.

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6 hours ago, ChappyMike said:

Hi Everyone - we had the IAC go out on one of our engines over the weekend. Does anyone know the part number? It's a 2003 MerCruiser 5.0 MPI. 

Also, I've read conflicting reviews about the OEM part and an automotive equivalent. Thoughts? 

Thanks!

Motorcraft CX1766 Idle Air Control Motor    W

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On 5/21/2018 at 7:00 PM, Wingnut said:

Motorcraft CX1766 Idle Air Control Motor    W

+1 I picked up one of those from Napa.Worked perfect half the cost of OEM. I even painted it high heat gloss black to match the motor. It is looks identical to the OEM IAC. That was two years ago. No issues.

:captain:

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On 5/21/2018 at 1:54 PM, SG Boater said:

I just put one on '05 5.0 MPI 2 weeks ago.  Works perfect.  

STANDARD MOTOR PRODUCTS

AC423

Idle Air Control (IAC) Valve

$ 41.79

$ 0.00

This is from Rock Auto.  If you put in the AC423 in has the #'s that this replaces and I believe one of those is actually the mercruiser #.  This particular # doesn't come with the right gasket however, comes with sort of a molded o-ring made to fit in a groove.  Either get the gasket separately from Rock Auto, or you can pick up at any auto parts for next to nothing.  I believe the Mercruiser is north of 100 deer for the IAC. . 

This one I have had a failure with. I've never had luck with Standard Motor Products, even back to the late 60's. Dang, I'm getting old.  W

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2 hours ago, Daytripper said:

+1 I picked up one of those from Napa.Worked perfect half the cost of OEM. I even painted it high heat gloss black to match the motor. It is looks identical to the OEM IAC. That was two years ago. No issues.

:captain:

Funny you mentioned paint. The Merc valves fail because they get too hot and I have a theory that they run cooler when left unpainted. Probably nothing to it, but I've replaced a half dozen on these things now , but have never done on the second time, and all were bare aluminum replacements, even the OEM Merc units. W

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1 hour ago, Wingnut said:

This one I have had a failure with. I've never had luck with Standard Motor Products, even back to the late 60's. Dang, I'm getting old.  W

I got an extra and will carry it along so won't get stranded, but will keep that in mind as the 1st thing to check if I ever have the symptoms again.

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2 hours ago, Wingnut said:

Funny you mentioned paint. The Merc valves fail because they get too hot and I have a theory that they run cooler when left unpainted. Probably nothing to it, but I've replaced a half dozen on these things now , but have never done on the second time, and all were bare aluminum replacements, even the OEM Merc units. W

Yep, wish I would have known about the Motorcraft one as my Merc part was over 100 deer. I was pretty new to my motor when mine failed at 350 hours, I had a 5.0 carb before it. New one is just non painted aluminum. The old one got hot around the area where the plug in is connected to the metal. There was a large gap in that area.

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Thanks for the heads up everyone. I ordered the aftermarket one with OEM gasket and will install and test this weekend. 

Dealer we bought the boat replaced the starboard one as it had failed, but left the port one. Low and behold, after only an hour of run time after buying it, the other one fails. Why the dealer didn't do both at the same time, I don't know, but at least it's an easy and relatively easy DIY fix. Also glad we had two engines and were only 1/4 mile from the marina so we could cruise back!

Thanks again everyone!

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7 hours ago, Wingnut said:

Funny you mentioned paint. The Merc valves fail because they get too hot and I have a theory that they run cooler when left unpainted. Probably nothing to it, but I've replaced a half dozen on these things now , but have never done on the second time, and all were bare aluminum replacements, even the OEM Merc units. W

Pretty sure my OEM replacement was also bare aluminum.  Guess they made a design change which would support your theory!

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On 5/23/2018 at 2:32 PM, TexasPilot71 said:

Pretty sure my OEM replacement was also bare aluminum.  Guess they made a design change which would support your theory!

Well my 496 was painted gloss black to match the engine from the factory. 2009 was the last year for the non catalyzed 496's. In fact they went to 502's in 2010. I painted the replacement and have had no issues. Then again I'm really bad about attention to detail so my wife says...:rolleyes:

 

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Ive replaced the IACs 3 times total on my 2 5.0 MPI's in 3 years.   Been working fine for a year now.  Last one installed was a Sierra, I dont remember what the bad ones were.

The failure mode is that they dont start with the throttle at the normal, neutral position.

However, when it wont start normally, I can press the gear release and it will start when the throttle is advanced (in neutral), and it will stay running when I put it back into neutral and then forward. If you are new to boating, make sure you know how to do this.

Your mileage may vary.

I have heard people say that they get dirty and stick.  Ive wondered if there is a calibration procedure to set the IAC signal which might help prevent the failures, but I never looked it up in the service manuals.

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8 hours ago, gr8lakes said:

Ive replaced the IACs 3 times total on my 2 5.0 MPI's in 3 years.   Been working fine for a year now.  Last one installed was a Sierra, I dont remember what the bad ones were.

The failure mode is that they dont start with the throttle at the normal, neutral position.

However, when it wont start normally, I can press the gear release and it will start when the throttle is advanced (in neutral), and it will stay running when I put it back into neutral and then forward. If you are new to boating, make sure you know how to do this.

Your mileage may vary.

I have heard people say that they get dirty and stick.  Ive wondered if there is a calibration procedure to set the IAC signal which might help prevent the failures, but I never looked it up in the service manuals.

There are two failure modes, one mechanical and the other electrical. The units mounted to the throttle body I've seen fail due to carbon build up, but it's rare and they can be cleaned if you are very careful. A quick visual inspection after removal will tell you if that is a possibility. The ones mounted remotely at the rear of the intake manifold are hose connected to the intake network and are protected by a small IAC filter which is located within the actual throttle body. For whatever reason, it's hot back there and the small servo motor can go up in smoke, sometimes failing in the closed position and sometimes failing open causing the condition you described. In a worst case situation, when the motor fails it takes the power feed from the ECM to ground, smoking the ECM also which becomes an expensive adventure. Poor design to say the least, but I've never seen that happen but a member here was unfortunate enough to have failed the ECM too. I guess the message is is you suffer a failure and need to limp home, it would be best to unplug the failed IAC until you are able to replace it with a new one. The ECM and PCM 555 processors actually spell out IAC failure on the Smart Craft alarm display, but only if the IAC fails electrically.  W

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14 hours ago, gr8lakes said:

I might have heard: "dont unplug the IAC when the key is on" lest the PCM gets damaged, but maybe i misremember.

It will set another code that will auto-clear when issue is resolved, but no damage.  W

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Like Wingnut mentioned, regarding the IAC muffler inside the throttle body, most people have no clue it even exists. It never gets replaced and gets full of carbon restricting the air flow to the IAC valve. I have spoken to mechanics that thought I was crazy when I mentioned the $1 part that never gets replaced, they didn’t even know about the muffler. I replace mine every year because it’s a heck of a lot cheaper than a new IAC valve. 

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9 hours ago, Supranut said:

Like Wingnut mentioned, regarding the IAC muffler inside the throttle body, most people have no clue it even exists. It never gets replaced and gets full of carbon restricting the air flow to the IAC valve. I have spoken to mechanics that thought I was crazy when I mentioned the $1 part that never gets replaced, they didn’t even know about the muffler. I replace mine every year because it’s a heck of a lot cheaper than a new IAC valve. 

Or throw it away and see if you can even hear any difference. Merc is turning the throttle bodies around facing rearward on some of their new engines, along with much more robust engine vibration dampening. Likely an attempt to compete with the newer 4 cycle outboards. Can't even tell they are running at idle.  W

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