2018 DF90 idle/low speed issue

[Frankp54]

So over the winter the engine sat longer than expected. I ended up having to replace the high pressure fuel pump in the vst. This fixed my issue of not starting, and the Boats been running fine so I took it out over the weekend. Towards the end of the day In a no wake zone Noticed the boat would have a slight miss almost at idle speed and was very hard to stay running at idle speeds. If I ran above 2k Rpms and WOT the boat runs great no issues. It’s the area above 500rpm when bumping into gear that i get the most issue. It’s a small hesitation. The only thing not cleaned was the injectors. Since the issue occurred I’ve Replaced the Spark plugs, drained tank, new filters. I’ve also ran it in the yard on an external tank. Seems to be a reoccurring slight rough idle but clears up with higher rpm range. Any help is appreciated!

[captainmike454]

Look at the Idle Air Control

[Frankp54]

Is that something that can be adjusted Mike ?

[captainmike454]

Your outboard is a 2018 so it should still be in warranty if you got the 6 year extended and trying to find a dealer to fix it is the best way to go although I have had bad luck personally trying to make that happen lately.

The IAC is not adjustable and $300 from Suzuki but can be cleaned with the correct sensor safe cleaner and replace the o ring .

There are aftermarket and car based Mitsubishi IAC replacements for a fraction of that but be careful in not doing anything to give Suzuki any reason to void your warranty.

[Frankp54]

Thanks for the input. Yeah it’s covered but was told it would be weeks out in my area for warranty work which is why I did the high pressure pump myself. I’ve ordered a new IAC and will go from there. Will I need to reset that sensor or will a new one clear any code ?

[Frankp54]

Little update I installed a new IAC sensor and it actually runs worse now and won’t stay idling. Also installed new injectors before installing the IAC and still had the same issue. Thinking about putting the old IAC back on and cleaning the vst tank again. The only thing that hasn’t been replaced is the rubber grommet inside the vst for the high pressure pump. Possible issue ?

[redlowrey]

Did you remove the inlet manifold when you done the vst, if you did you probably have an air leak at on of the runners. That will make the engine run rough at idle and not noticeable under load or high rpm.
Bring the rpm up with the warm up leaver and remove each coil connector one at a time and see if you can locate which cyl makes no change when you remove the connector.

[Frankp54]

I did remove the intake but I’ve sprayed around the runners of the intake to see if I had any rpm drops or increases and I don’t have any.

[redlowrey]

Run the engine and see if you can pick which cyl is not working or their all erratic, plus pull the vapor line off the top of the vst and see if any fuel comes out. It seems like your a tinkerer so you should be able to tell if you have a single cyl miss or one that is effecting all cyls.

[catacom225]

I would also check and see if your fuel tank is venting and not restricted in any way