Mercruiser Scorpion 330hp idle

Postby Feetfirst » Wed Oct 28, 2020 1:52 pm

Hey guys, went to the river yesterday and noticed that my engine idle dropped to about 200rpm twice while stationary. It only last about 2-3 seconds, no alarms, came straight back to normal idle after that. No issues with power while skiing or “at speed”. Has anyone experienced this before? Bit of history, new iridium plugs 2 years ago, new fuel filters, tank clean, hose etc about 6 months ago. My first thought would be possibly the fuel pump failing but there’s no sign of anything at full speed.
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Re: Mercruiser Scorpion 330hp idle

Postby will » Tue Nov 03, 2020 8:14 am

Any luck mate? What fuel do you use?
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Tue Nov 03, 2020 12:00 pm

Hey will, fuel should be fine. I generally use 98 and 95. It doesn’t appear to be doing anything strange when under load. I’m going to change the plug leads to start, it’s really the only thing I haven’t changed over the last few years. Might be a core collapsing?????? Being a 06 model they may be the original ones so would be due for a change.
Have you been getting out?
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Re: Mercruiser Scorpion 330hp idle

Postby will » Wed Nov 04, 2020 8:24 am

Good call. At the very least it probably needed to be done and eliminates a suspect. I got out behind a mates Mal 4 weeks ago, but nothing since. I'm working on a big project that should hopefully help me get my wake fix as often as possible :)
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Re: Mercruiser Scorpion 330hp idle

Postby lewy71 » Thu Nov 05, 2020 9:14 am

The dissy cap is a known problem area with the Merc inboards but your symptoms does not really fit. Plug leads and dissy caps usually breakdown under load not at idle.
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Thu Nov 05, 2020 7:26 pm

Yeah lewy, looking further into it I think your right. They are old anyway so it won’t be a waste. But with looking further into it the air control valve (IAC sensor) directly controls the idle so I will change that too. The OEM part is $225 so again not a big purchase.
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Thu Nov 05, 2020 7:27 pm

You can’t stop at that Will, “big project”. What are you up to?
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Re: Mercruiser Scorpion 330hp idle

Postby lewy71 » Fri Nov 06, 2020 8:12 am

Try giving the throttle body and the IAC valve a clean before replacing. The screens on the IAC's can get blocked.
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Fri Nov 06, 2020 8:17 pm

Thanks Lewy, I’ll give that a go.
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Mon Nov 09, 2020 8:04 pm

318AE97F-FEFE-4C0B-8916-7D7894E786D9.jpeg
92B209B9-0B52-424C-92FE-DC0233F4B24E.jpeg
F78D8027-A266-4AD9-8F58-DB1C1F0044E7.jpeg
92D29345-C863-453D-8B88-7036FE70B4C3.jpeg
9ADA7AA6-CD47-4CFA-BFBF-A880807E7568.jpeg
B93C9004-381C-4406-BDE2-664C85AFB858.jpeg
So I pulled the plenum off, if anyone plans on this there are two bolts underneath at the front of the plenum that took some finding. Pulled the IAC sensor, found it filthy. There was a fibre gauze in there that was chockers and the S/S mesh was also pretty blocked. The sensor valve itself was moving but very notchy. I cleaned all that with solvent, lubed the spindle and cleaned the gauze etc. with everything clean I reassembled. Will give it a run on my next days off and let you all know whether it worked. Photos from bottom to top.
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Re: Mercruiser Scorpion 330hp idle

Postby will » Wed Nov 11, 2020 8:50 am

Feetfirst wrote:You can’t stop at that Will, “big project”. What are you up to?

PM sent mate :)
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Wed Nov 11, 2020 3:57 pm

So I ran it on the trailer. Very noticeable that it started easier, waited till warm and did a few out of gear high rev’s back to idle. Definitely stronger idle, it use to hunt a little bit before and that completely gone now. On a side note i also received the plug leads so changed them as well, before there was a constant “ticking” which has also completely gone. Going to the river tomorrow so that will be the real test but happy with the difference so far.
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Thu Nov 12, 2020 10:18 am

Did a river test this morning, stoked to find that the idle issues are completely gone. Starting heaps better and generally appears to be running better overall. Thanks Lewy71, you saved me a few hundred.
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Re: Mercruiser Scorpion 330hp idle

Postby will » Thu Nov 12, 2020 1:53 pm

Awesome!
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Fri Nov 13, 2020 1:28 pm

PM sent will.
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Re: Mercruiser Scorpion 330hp idle

Postby mof » Fri Nov 13, 2020 2:40 pm

What was that rubbish in there? How does it get in there?
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Sat Nov 14, 2020 12:40 am

Hi Mof, it was a build up of very fine dust. When it got wet with the solvent it basically dissolved. When I tipped the solvent out of the container it was like sludge in the bottom. I guess without a proper air filter there’s nothing to stop the smaller particles.
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Re: Mercruiser Scorpion 330hp idle

Postby Feetfirst » Sat Nov 21, 2020 5:26 pm

Another morning on the river and the idle was solid. Starting better as well. Well worth the effort if yours is getting a little lazy on the idle.
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