Engine will not idle 5.0L Merc

Presentation

Presentation

Well-Known Member
TECHNICAL Contributor
Oct 3, 2006
4,404
Wisconsin - Winnebago Pool chain of lakes
Boat Info
280 Sundancer, Westerbeke MPV generator
Engines
twin 5.0's w/BIII drives
We have engine troubles. It started yesterday.

Our starboard engine will not idle. :smt100

If I disengage the drive and move the throttle up a bit I can start it at higher RPM's and can slam it into gear by doing a fast pull back and push forward of the starboard throttle but as soon as we slow down this engine shuts off. The engine just does not hold idle. As long as I keep it above about 800 RPMs it runs. Below that it dies.

I opened the hatch but could not find a big “on / off†switch in the off position :huh: so after checking the fluid levels, trying to justify why I opened the hatch in the first place, I closed it back up.

Oil and temp are fine. When the engine is running, everything is normal.

The power steering is on the starboard engine so with this engine off steering was difficult and slow.

Another member of our marina must have sensed something was up because when we came into dock he ran over and gave us a hand. Great guy and I own him one for sure.

I will be calling the marina to take a look at it.
 
Sorry to hear you are having engine trouble. mine started showing something like that just before an alarm went off. it was the IAC valve. we have the same year boat and those valves last about 3 years (at least that's what I was told). both of mine are now replaced.
 
That sucks, would be nice if they made powerstering redudent in cases like yours.

I'm no boat expert but on twin engines don't you have sperate fuel pumps and filters. Sounds like a similar problem we had in our old Tahoe which ended up being the fuel pump.
 
Welcome to the bad IAC club. I had this happen to me on my 5.0 on my 240SD and wow what a job trying to get it back into the dock.

It an easy thing to replace and is right on top of the intake manifold. In fact I am going to buy a spare one for my boat this week as I can't imagine trying to dock my 260DA with a single engine if it wont idle. :wow:
 
Dave S said:
Welcome to the bad IAC club. I had this happen to me on my 5.0 on my 240SD and wow what a job trying to get it back into the dock.

It an easy thing to replace and is right on top of the intake manifold. In fact I am going to buy a spare one for my boat this week as I can't imagine trying to dock my 260DA with a single engine if it wont idle. :wow:
Click to expand...

hehe now you got me worried, where you buying from and how much is this gonna cost me. I like having extra parts. My wife thinks I'm nuts. I bought back of every fuse on the boat and light bulbs.
 
Morpheus...........Sea Ray supplies extra fuses with the boat. Look in the black Sea Ray bag.

As far as "spares" go, have on board what you think you might need in case you have a problem on the water and can't get back to your dock. In some instances though it may not be practical to try on the water repairs. So in my opinion the most important thing to have is a VHF radio to call for help or a tow if needed.

Now let's get back on topic here and let others respond about Presentation's idle problem.
 
I think it's unanimous, that is what is sounds like to me. If I were you I'd replace both of them.
Sorry for your trouble but his one seems like it's a simple fix.
Hope that's it and best of luck

:cool:
 
The IAC valve is in stock at the local dealer. $91/each.

I will buy two, change out the one then go for a test run.

I will update this post once done.

Thank you all! :thumbsup:
 
don't forget to get the gaskets too.
 
Also check the IAC Muffler. It is a $1.50 piece of foam about the size of your thumbnail that sets in the throttle body. You can easily see it when you take off the spark arrestor. It filters the air going to the IAC valve. If it's dirty it will screw up your idle like having a bad IAC.
 
Sorry I did not get the last two replies until I got back.

Changing the IAC did it. It works now. Thank you!

Gasket? I did not see one. I did not see one on the old one either.

Foam piece? I did not see one. I did not see one on the old one either.

I did buy 2 intake air control (IAC) valves. I only installed one. The Allen wrench size was odd. I did have it but had to grab my old big loose Allen wrench kit I normally don’t use. Good thing I had it along in the car. I kept this specific one onboard incase the other IAC on the other engine goes out.

Again, thank you!
 
I'm with you-- same problem on my 320. Replaced it for $80 and got a spare! Wasn't sure though- so had the marina test it- not sure what that will cost me. Now I know the next time. I'm told they "go" all the time.
 
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