Low and Rough idle on 04' 320 DA w/ 350 Mag

C6 Doberman

C6 Doberman

New Member
Jun 10, 2009
106
ga
Boat Info
2004 320 Sundancer
Engines
Twin 350 Mag. V-Drives
I thought I had a trans issue because the trans was clunking and making noise but then I noticed the engine was only at 350 rpm. Trans sounds normal when you idle the engine up to 600 rpm where it should be. I replaced the spark plugs and still have a rough idle. I don't see individual coil packs just a distributor on the back of the engine. Are these digital or do you have to replace the rotor button and what not on these? Where else should I look. Dealer is suppose to get down with a scanner to see what the alarm is. Just trying to narrow it down myself.
 
The rotor and cap can and should be replaced if it has not been. My cap and rotor were corroded pretty bad. When is the last time you changed the IAC? I guess this is just happening on one engine?
 
I bought the boat last year so I haven't changed it and from the way everything else has been it is probably the original stuff on it. It is just the port engine now but what ever I replace on one the other is getting it too.
 
Presentation has a good write up somewhere on how to change the cap and rotor. It is very simple. If you don't have the maint records you should consider changing them as well as probably the plug cables.

You could possibly swap the IACs between the engines just to rule out an IAC issue. You may need to purchase 2 new gaskets at the dealer though when doing this but they are only a dollar or so each.

Where in GA are you?
 
Thanks Jason! Where are the IAC's located. I know its probably a dumb question but I have never had an issue with one so I don't know where it is. I changed the impellars on both engines and the spark plugs. I guess I'll get the rest of the ignition system too.
 
Whether you end up changing the IACs or not, be sure to replace the IAC mufflers. That could also be the problem with your engine. The IAC muffler is outlined in the article I just posted. They get dirty and can cause problems such as you have described. I replace mine every 8 months just to keep them clean and because it may very well be the cheapest part on the engine.
 
Thanks for all the help! I am on Lake Lanier by the way.
 
The IAC is on the top of the engine connected to the air breather.

I found the IAC valve on the Internet for about $87. MarinePowerService.com (See receipt below) I also bought a few extra gaskets and mufflers. The muffler is small 3/4 inch piece of white filter (looks like the same material you would see on a floor buffer) I bought 2 IACs and will keep one on the boat as a spare. Remove 2 allen screws and and unplug the wire attached to the valve. You may need a utility knife to cut the paint to separate it from the base it sits on. The total job was 15 min. Seems to me that Mercury should be giving these items away with an apology letter.

The part # below is for my 6.2l engine, not sure if it is the same for the 5.7


SKU #: 35-863829
QTY: 6
ITEM: MUFFLER-IAC
PRICE: $1.06
------------------------------------------------------------

SKU #: 27-863112
QTY: 3
ITEM: GASKET
PRICE: $1.04
------------------------------------------------------------

SKU #: 862998
QTY: 2
ITEM: VALVE, Idle Air
PRICE: $87.40
------------------------------------------------------------
 
well the dealer called and confirmed that it is the IAC valve. Ordered two and will be in tomorrow. Thanks for all the help guys. This forum is golden!!!!!!
 
Replaced both IAC's Friday and all the spark plugs. Boat runs like I champ now. Nice smooth idle and throttle response. I was surprised to see that the boat still had the factory IAC on it. Still painted black like the rest of the engine. Boat is an 04' with 350 hrs. Thanks for all the help and once again this forum proves to be priceless!
 
C6 Doberman said:
Replaced both IAC's Friday and all the spark plugs. Boat runs like I champ now. Nice smooth idle and throttle response. I was surprised to see that the boat still had the factory IAC on it. Still painted black like the rest of the engine. Boat is an 04' with 350 hrs. Thanks for all the help and once again this forum proves to be priceless!
Click to expand...

Glad you got it running well again! You definitely got your use out of those IACs if they were original. Be sure to replace the IAC mufflers on a regular basis and that will help extend the life of your new IACs.
 
Thanks Jason. I changed them out with both the IAC's. They were pretty nasty!!!
 
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