Rough Idle - Injector Issue?

Our boat is a 2007 Sanger V230 w/5.7 'black scorpion' engine. It only has 169 hours on it and it's running pretty rough.

Last the boat started idling poorly and would die when you put it into neutral. I found that emptying the fuel/water separator helped the problem temporarily but that never lasted more then a couple of engine hours. Nearly every time we used the boat I was emptying the fuel/water separator. At the end of last season I drained the fuel tank, filled with fresh gas, and it was running almost back to normal (say 95% normal). On the last trip out to the lake I ran the boat out of gas. Luckily it died right as I was pulling up to the gas dock so it didn't ruin the day. Once I filled up with gas, the boat was back to idling like crap.

Fast forward to this spring, I take the boat to our mechanic and he checks it over, scans the engine for codes, empties the fuel/water separator (no water in it), and changes the spark plugs because they were fouled. He ran the boat for a minute on a fake-a-lake and the rough idle was gone. He said to put some time on the clock and if the problem came back then we most likely needed to have the injectors pulled and cleaned/rebuilt because the water in the gas last season likely clogged them. I'm not really mechanical so I have no idea if this is a common issue or problem? For a boat with such low hours I wouldn't expect to have to an injector issue, but I really don't know...

Pulling the injectors and having them cleaned/rebuilt will cost a pretty penny and I don't want to spend that money if I don't have to. Does anyone have any suggestions or thoughts on what our problem(s) may be and to fix it?

btw - I have no idea where the bad batch of gas came from (assuming that's our problem). We treat our tank every winter when we put it away.

Just do it. Small price to pay compared to the cost of the boat

Would a bad IAC Filter be of concern?

dump a couple cans of seafoam in there

Your gas likely has alcohol in it. Use the Blue marine Sta-Bil in every tank and your problem should go away or be significantly reduced. Some areas, like mine, have "recreational gas" for boats and other engines that do not like alcohol. The injector may be an issue, now. However, the Blue Sta-Bil and a couple bottles of Techron may take care of the issue on the cheap.

Sea Foam is great, but it does not stabilize the alcohol/water issue as well as the Sta-Bil. It does, however, work about the same as the Techron.

So you changed the spark plugs - were they gapped correctly.

Also, were the cap and rotor changed simultaneously with the spark plugs.

My suggestion would be cap rotor and check plug gap.

I have got in the habit of replacing both fuel filters, Cap, Rotor, Plugs at the beginning of each season. I can go to Napa auto parts and pick all that up for $60. With as much moisture that is in the boat - the cap and rotor tend to rust pretty quickly and can cause poor spark and in turn cause a rough running motor.

btw - my engine is a 97 indmar monsoon with close to 1000 hrs and I have never had the injectors serviced. It runs smooth as silk

I would agree with Murphy. I would replace the cap and rotor. I had the same issue last year and this fixed my problem. I have an 05 indmar assault.

Third vote here for the seafoam! That product has done wonders for me over the years. It has gotten cars to pass smog, cleaned carbon on the dirtbikes, boats, trucks etc.

If all else fails once you've replaced the cap, rotor and its down to the injectors id buy a new set opposed to having them rebuilt. Also this is a fairly easy task on our motors so you can save a few bucks and DIY.

Thank you all for the replies!

Adam - shove it

Jay - Where is the Idle Arm Control filter and how would I go about changing/fixing it?

Nate's - I put Startron (blue stuff) in with every fill up now. I plan on buying some sea-foam and putting it in the tank this weekend.

Murphy & Phil - I will check on the cap/rotor. Dumb question here, but I've never done a cap/rotor on a boat. Do I have to buy marine parts or can I pick them up at the local auto parts store? I have no idea if he gaped the spark plugs correctly, but I would assume (hope) so as he is a good mechanic.

Our last boat had 600 hours on the clock when we sold it and ran like new. I sure hope I can get this problem sorted out easily. Again, I appreciate everyones responses!

Rough idle on an EFI motor is usually the IAC, but Google found this: http://forums.iboats.com/showthread.php?t=262503&page=1

Not familiar with your motor, but the IAC should be a plastic cap on the side of the throttle body with an electric plug going into it. Pull it out and clean it up.

Patrick - you can buy the cap and rotor at Napa or any other auto parts store.

Make sure that it has brass contacts as they will hold up to the corrosion much better. Also make sure that you get the plug wires on the same studs when going from old to new.

Best thing to do is move the plug wires one at a time. Plug wires wear out too after a few years and can affect idle.

Finally had a few minutes to get to the boat tonight and I started trying to pull what I think is the IAC valve. I unplugged the wires and pulled the cap. I think that the valve is still buried in the air filter (not sure what it is) because I found another pic on a Tige forum of someone with a similar problem. Anyways, here are the pics I took

I'm not familiar with Sanger/Merc but that looks more like a Throttle Position Sensor.

Do you have anything that looks like this in the area:


That's supposedly a Merc IAC but I'm not sure if it's applicable to your particular engine.

BTW your pics above are definitely of the TPS:
https://www.skidim.com/prodinfo.asp?number=R020040

I found these picture on a Tige forum when I Googled IAC valve. If what I pulled is the TPS then I have no idea where the IAC valve is.

These aren't my pics, but this is a Merc engine...so it should be similar to mine...?

I appreciate everyone's help! I'm looking to get out on the water 2 days this weekend and would love to get this taken care of before then!

It has to be somewhere on the throttle body.

On the way home from work I stopped by my mechanic (without the boat) and asked if he could show me where the IAC valve is. He didn't have any boats with Merc, but he had a Nautique and showed me where to find it. Got home and I couldn't find it anywhere! I took all sorts of stuff apart and even looked up a Merc manual that showed where the IAC is supposed to be. On my engine it's not in that spot!

I think I found where it is (on the port side of engine under the the air intake/cover) but I didn't want to pull the cover off because there appears to be a gasket and I know sometimes you have to replace gaskets once they are removed...plus I'm not even sure taking the cover off will show reveal the IAC valve.

I'm just going to take the boat to the mechanic next week

I finally found it! I was able to get a manual for the engine on-line. Pages 107-109 explain how to get to it. It's definitely not in the normal place most engines have it.