DF 175 RPM issue

[Joe buchanan]

Hi all.
I have twin 2008 DF 175’s that are acting up. The problem is intermittent. Some times both engines will do it. Sometimes just one, and sometimes not at all. The engines start and idle fine at 650 rpm each and run smooth with great performance. The problem starts when you pull back to idle. When you shift into neutral the engines will start to surge up and down, up and down in rpms from very low to 2000+ and eventually shut off. When I restart them everything runs as normal. Please help!

[Hoosmatroos]

Are there any codes stored?

[artdf175]

Joe were you able to get this resolved?
what ties the electronics of your engines together?

Art

[Joe buchanan]

I have not been able to resolve the problem. In fact it has gotten worse. I cant think of anything that really ties the two engines together with the cat they have two completely separate batteries, fuel tanks and ignition. I was out 50 miles offshore a couple days ago when I stopped and noticed the starboard engine sounding terrible and shaking sputtering and rattling. I turned it off and back on and it ran perfect! sometimes when I would stop the boat one or both engines would surge up and down in rpms and cut off or eventually regulate. If I turned them off and restarted it went away. Other times I would stop and both engines would idle normally

[Moonlighter]

To me, this suggests an electrical issue. The chances of something else affecting both engines where there is independent fuel tanks seems less likely. Mind you, this would not stop me from changing out the water separating fuel filters between the tanks and engines, just to be safe.

We know that these engines do strange things, throw phantom codes, and do not run well when:

- there is poor voltage to the battery sub wire (the “white wire”), so look at the connections for this wire, look at the condition of the wire itself, undo and clean all connections to this wire. There is a splice along the harness and if you read the “sticky” about white wires on this forum, you will find more info about how to find it and how it can get corroded if poorly installed in a place where it can get wet.
- Also, the master battery switch itself can be a source of voltage issues, so again, undo and clean all connections and ypu may need to go as far as pullingnit apart to inspect and clean. Any doubts - replace this switch.
- the batteries and engine cables themselves - make absolutely certain your batteries meet the specs for yout motor as per the owners manual. Make sure they are charged up and are effectively holding their charge - have them load tested!!
- Check the battery cables to the engine and switches, all of them, undo, clean, check the cables for internal corrosion (a cable corroded internally may feel hard or crunchy when flexed) and tighten up.

[artdf175]

so both engines are completely independat and there is no place the wiring can cross over from one side to thd other ?
each on its own electrical master switch
each has its own ignition switch and remote for shifting and throttle ?
If one battery died you wouldn’t be able to start that engine?
just tring to see if there is anything common t

How about fuel?
The IAC valve regulates the idle speed and the ‘dash pot’ effect when coming back to idle

Art

[Joe buchanan]

Thanks for the reply’s. There is an on off switch that allows you to cross over the power from the port battery to the starboard in the event the starboard battery dies. I will remove and clean this or replace and remove and clean both white wires and test. Right now I’m leaning towards the iac being the culprit

[Murray]

Two IAC valves acting up at the same time. What are the odds of that happening? Not a very constructive comment but it would be one heck of a coincidence. Art mentioned fuel, could you have purchased some bad fuel?

[Joe buchanan]

So I pulled both batteries and cleaned all connections well including the white wire which is connected directly to the + post as it should be. No change. I then pulled The starboard IAC Valve and cleaned and re-installed it. I went offshore and caught some dorado. Once the port motor started the revving and cut out but the starboard that I cleaned the IAC on didn’t do it. Since it is random and not always both engines this is not a cure for sure?? Today I pulled the other IAC and will test both engines this weekend and report back. thanks for the reply’s

[artdf175]

Joe did you check your fuel? I didn't see made any references to your fuel
I would suspect you should have a fuel/water filter. you might pull the filter off and dump contents in a clear jar and see if there is any water/gunk in it.
doesn't take much dirty fuel to create problems.. another place to check is the small fuel filter pre low pressure fuel pump. any dirt/water in that is a big problem.
and if you have to use the alcohol laced road fuel, it had a way of breaking down and creating havoc, especially with our outboard motors
Art

[tsturm]

Two IAC valves acting up at the same time. What are the odds of that happening? Not a very constructive comment but it would be one heck of a coincidence. Art mentioned fuel, could you have purchased some bad fuel?

Similar Hours? The only issue I have had with my DF175 is very similar to the original poster's. I removed the IAC & cleaned it and all is well! I now remove & clean the IAC yearly. (My DF175 has 1620hrs now.)

[Joe buchanan]

Update...
I removed and cleaned both iac valves and reinstalled. Ran out to the backside of San clemente island yesterday which is a good 80 mile run with many stops. Engines ran flawlessly problem resolved by cleaning the iac valves

[Murray]

Thanks for the update.What did you use as a cleaning agent?

[Joe buchanan]

I actually didn’t use anything just a little water and a microfiber towel