350 EFI mercruiser idle.

gish498

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Ok I got one for you guys. I have just became a first time boat owner. When I went and looked at it everything seemed fine. I took it out with an experienced boater and all was goin good until I went to trailer the boat. It runs good above 1200rpms but will not idle right. The motor was just put in the boat about 3years ago. I put muffs on it in my driveway and started it and it ran fine for about ten minutes so I turned it off. A friend of mine came to look at it and wanted to hear it run so I started it back up. It will idle but spattically. It tries to die and then revs up to 1000rpms and then sinks again and then revs back up. I am somewhat mechanically inclined but am new to fuel injection and boats. Any assistance would be great.
 
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TilliamWe

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Re: 350 EFI mercruiser idle.

IAC. "Idle Air Control" would be my first guess.
 

Jono69

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Re: 350 EFI mercruiser idle.

Can you please clarify what "I put nigga on it" means?
 

gish498

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Re: 350 EFI mercruiser idle.

Yes I would like to apologise for that. I typed muffs and it autocorrected to that. I am sincerely sorry. I will try that
sensor. Thank you very much.
 

Don S

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Re: 350 EFI mercruiser idle.

Before you start throwing parts at it, why don't you do some troubleshooting.
Since there are a bunch of different EFI systems, on 5.7's, post a Merc serial number so we know what you have.
 

Jono69

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Re: 350 EFI mercruiser idle.

Yes I would like to apologise for that. I typed muffs and it autocorrected to that. I am sincerely sorry. I will try that
sensor. Thank you very much.
I had to give you a hard time for that! Don't be sorry! Haha! Best of luck with your boat issues. I'm sure Don will get you going in the right direction.
 

gish498

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Re: 350 EFI mercruiser idle.

I will get a serial number as soon as I get home. I appreciate the help and you are right I don't wanna start throwing money or parts at it.
 

sasada

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Re: 350 EFI mercruiser idle.

It tries to die and then revs up to 1000rpms and then sinks again and then revs back up. I am somewhat mechanically inclined but am new to fuel injection and boats. Any assistance would be great.

My 5.7L (also fuel injected) volvo is doing the same thing to a lesser extent! Mine will stay at high idle after chugging a little bit at idle. After i kill the motor and restart it, it will idle fine. Don S. (knows a TON about I/O's!) recommeded i put a scanner on mine...however i called and its $90 just to hook it up and $400 if i wanna buy on. Best of luck!...PLEASE keep us updated!
 

gish498

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Re: 350 EFI mercruiser idle.

Ok here is the serial number. 0F422968. I hope this helps. I want to take it somewhere but I have a fear of shops working on something that I don't know much about. Plus I own a boat now so I'm broke lol.
 

gish498

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Re: 350 EFI mercruiser idle.

Thank you Don. I will do some reading. In the mean time is there anything I should look for?
 

Thalasso

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Re: 350 EFI mercruiser idle.

IAC. "Idle Air Control" would be my first guess.

A bad iac won't let the engine idle at all. You can take a ohm meter and check it. You should get at least 7- 100 ohms for it to be good. If you do change it don't forget to put a new muffler in.In fact i just installed one yesterday for someone on a 350.
 

Don S

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Re: 350 EFI mercruiser idle.

His system doesn't have a muffler.
 

gish498

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Re: 350 EFI mercruiser idle.

Ok guys. This afternoon I had some time so I started looking some things over that I read in the link Don sent me. I put new plugs in checked the oil and power steering fluid, things of that nature. I did not notice anything out of the ordinary except the hose coming out of the valve cover ran up to the bottom og the air filter and did not connect to anything. I started it up for a minute and nothing has changed. Oh I gapped the spark plugs to .040 because I couldn't get a real good answer on where they should be.
 

Don S

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Re: 350 EFI mercruiser idle.

Oh I gapped the spark plugs to .040 because I couldn't get a real good answer on where they should be.

You have the manual, look at page 1B-8. It's .035.

Did you check your water separating fuel filter for water. Not just change it, actually check the contents.
Compression check? Fuel pressure checks?

That hose going to the flame arrestor does nothing but recirculate the air from inside the engine out of the engine compartment through the intake. Not part of your problem.

Do you have Champion spark plugs (Yes, that could be your problem)
 

Pete104

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Re: 350 EFI mercruiser idle.

Have you checked your distributor cap?

As suggested, don't use Champion spark plugs!
 

sethjon

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Re: 350 EFI mercruiser idle.

You have the manual, look at page 1B-8. It's .035.

Did you check your water separating fuel filter for water. Not just change it, actually check the contents.
Compression check? Fuel pressure checks?

That hose going to the flame arrestor does nothing but recirculate the air from inside the engine out of the engine compartment through the intake. Not part of your problem.

Do you have Champion spark plugs (Yes, that could be your problem)

Don, you're always knockin' Champion plugs. I wanna know why? I've used them in so many applications and never had a problem. What problems have you had?
 

Don S

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Re: 350 EFI mercruiser idle.

Don, you're always knockin' Champion plugs. I wanna know why? I've used them in so many applications and never had a problem. What problems have you had?

Not firing/misfiring many times, porcelain blowing out of the plug body several times, they are also longer which makes them difficult to change on some engine. Other than that, no reason.
 

gish498

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Re: 350 EFI mercruiser idle.

The plugs I put in are autolite with copper core. Like I said I am new to the whole boat thing so I don't know what it good and what is not. I work on dirt bike motors a lot and since this is a new and totally different animal I dont wanna mess anything up. I have never had to do a compression check anything and would not know for sure how to do it. I am goin to check the distributor today as well. I guess i am just use to dirt bike engines. When there is something wrong with a bike it is a problem from the get go. I am still confused why sometimes this idle issue is a problem and other times it idles fine. I do appreciate your support and your help so keep guiding I will be forever grateful!
 

gish498

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Re: 350 EFI mercruiser idle.

Ok I think but am not getting my hopes up but we may have progress. I regapped the plugs to .035 and removed the distributor cap and cleaned the profs off and fired it back up and instead of the idle goin from almost dieing to around 1500 rpms it just bounces between 800 and about 1100 rpms. Having said this do you think it was the gap or the distributor cap? I was goin to check the compression but was told if that was bad that it would not run good no matter what the rpm. is this true?
 
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