Idle Issues, 2007 115 HP Mercury Optimax DFI 2-stroke

[Driftfishing]

*****Boat and Motor information:
2008 Nitro Z591 18’ Bass Boat
Motor: 2007 115 HP Mercury Optimax DFI 2-stroke
Serial # 1B482113
115ELPTO
Original Issue: After winter storage with fuel stabilizer and battery charger plugged in, engine ran roughly and would not idle correctly (stalling) or go over 5000 rpm.
Spark jump was checked, ok on all cylinders. Fuel filter was changed, hand-pump fuel bulb changed, connections on fuel lines tightened, fresh gas added, plugs were changed. Engine ran better but would cough and stop while idling.
Spark jump distance was checked again, now cyl. 2 was weak (under 1/8”). All coils were changed, spark jump was fine afterward. Engine ran smoother 1200 RPM and above but would cough and stop while idling.
Fuel line was removed from tank, placed in fresh 2-stroke pre-mix (50-1), to check for air leaks or bad gas. No change, engine would still cough and stop while idling.
Engine was run at ~1200 rpm. One by one, each of the plug wires was removed. Engine stopped after cy. 1 & 3 wires were removed, not after cyl. 2 wire was removed. All air and fuel injectors were sent out for service check and cleaning. Engine ran much better above 1000 rpm but would still cough and stop while idling.
Air and fuel rail pressures were checked with engine running at ~1200 rpm. Fuel was ~115 psi and air was ~95 psi. Also, fuel-smelling grey fluid came out of the air-port along with air and mist. Online forums indicated (wrongly I now know) that this was high pressure on both test ports, indicating that (due to high pressure and fuel in the air rail) both the fuel and air pressure diaphragms were leaking. I have gray air injectors, and other forums indicate that these pressures are ok for gray air injectors, but fuel in the air lines is not ok. I spent $200 each on two new purple diaphragms and $95 on an installation tool, which did help a lot as far as installation went. Engine ran much better but would cough and stop while idling.
I am going to get off track from the analysis to vent for a moment: A recreational craft that goes out on the water and risks people free time (and lives) should be as reliable and complicated as my lawn tractor. If the Nanny government and the EPA would get out of everybody’s kuesters we might be able to do that, and that includes a universal cuss-out to those who promote ethanol in the gas that absorbs water and eats and corrodes boat motor components. I’m an old R&D engineer and I can’t get my G’damned Optimax boat engine kit to work properly, how the hell will Joe six-pack do it? How am I supposed to figure it out after a six-pack or two? To their credit (Mercury) it worked 11 years flawlessly, is it throw-away now? Ok, onward:
I re-checked everything with better info and gages, and realized the fuel rail pressure (108 psi) was ok, the air rail pressure (94 psi) was ok, giving a differential of 14 psi. And my Optimax 3-cyl 115 HP has no tracker valve, not anywhere. So many different engines, so many different years… so many stories. BUT, there was still a fog coming out when depressing the high pressure air shrader valve, and a cough and stall on idling. This, the forums attributed to water in the high-pressure line, indicating a problem with the high-pressure air pump. (or possibly high humidity). I took off the head of the air pump, found moisture and corrosion, and got two new gaskets, cleaned the surfaces, and gave it another try. No change, cough and stall on idling. Maybe ran a bit smoother at or above 1000 rpm.
Re-checking everything, the air rail still had some water fog when pressing the shrader valve. Some people say this is normal, I don’t have enough experience to tell. However, I did notice that if I keep pressing the air valve button every 15 seconds, the engine does not stall. Does the moisture build up? From where? Is this a clue? I did re-check the surfaces on the air pump again in the morning, scrape them and re-assemble. I suspect continuously venting air just makes more fuel come out, and the richer mixture for some reason keeps it running. Fuel issue maybe?
With all these symptoms, the online wisdom suggested there was a broken reed valve. So, I took off the oil reservoir (major PITA, maybe not if the lower engine cowlings were removed first, another PITA I suspect), and the intake manifold, and looked at the reed valve inlet sides. Nope, no broken reed valves.
Another online suggestion was that the throttle position sensor was a probable cause, which could throw the timing advance all over the place. I looked up how they work: Three wires, one 5 V supply voltage, one ground, and one output. On cars, closed throttle is under 1 V, full throttle near 5 V, and no erratic behavior is good. Yes to 5 V supply, yes to ground, and the output voltage was: .425 V closed, 1.75 V mid throttle, 3.3 V high mid throttle, 4.21 V full throttle. Seems to work, seems unlikely to keep it from idling, although ½ V low across the range, maybe normal for Opti?
Hey if anyone can send me a pdf of a service manual for a 2007 115 HP Opti I could check and I would really appreciate it. On that note, how much does it cost to purchase and hook up the Mercury software to get some error codes? Simple with cars, apparently not with Mercury outboards. (additional dealer profit? Additional lost future customers?) sanfordmj11@gmail.com
So I did another engine check at 1200 rpm, removing one spark plug wire at a time. For each cylinder, if the wire was removed the rpm’s would drop and the engine would die. I think this means they each had spark, fuel, and air pressure. Still no idling for more than 30 seconds.
Another online search found a YouTube video on a similar 115 optimax that had a similar idling issue. The guy described taking apart the fuel supply, the three fuel pumps (four counting the hand bulb, the crankcase pressure driven primary, the low-pressure electric, and high pressure electric fuel pumps). So like him, I took it all apart, cleaned it all carefully, put it together. Fuel pressure checked out ok (108 psi). Maybe it ran smoother above 1000 rpm, still coughs and dies when idling.
If any of you out there have an idea, please jump right in now. Right now, I’m looking for a computer diagnosis to maybe point me in some direction. Somehow, we have added electronics sensor issues, electronics reliability issues, software issues, moisture and corrosion from water-attracting ethanol, and green social issues, to the outboard motor, with predictable results (motor will not run). I would rather burn a little more fuel, make a little more smoke, and pay a whole lot less to enjoy my hobby.
Thanks!

[Capt.Insane-o]

Load test the battery.

[Driftfishing]

Load test the battery.

Thanks, not the issue here. 13+V, fully charged, not old, and cranking the starter hard.

[Capt.Insane-o]

Well okay.. you fixed everything that isn't wrong with it so I'd just trade it in on a new one.

[half fast]

May try opening the plug gap to approximately .042 it does help the larger 3.0 liter motor. Hf...

[Driftfishing]

Well okay.. you fixed everything that isn't wrong with it so I'd just trade it in on a new one.

Lol well there was the weak coil and an injector issue and a leaky fuel diaphragm and it does run better over 1000 rpm. Multiple issues point in a lot of directions, now I know a lot of common issues that are not causing this idle problem. I will load test the battery and check voltage at a few locations on the motor. Thanks for the tip.

[Capt.Insane-o]

I see you are in Maryland, if this motor is used in saltwater inspect the wiring harness from the fuse holders to the coil connections.

[Driftfishing]

Thanks all for the help. Here is an update and the final result/solution:
The battery, a blue optima, checked out ok.
Voltage while running was good, 14.49V at the alternator and multiple points around the engine.
I checked the crankshaft position sensor, 330 ohms across the two wires, ran out of hands and could not check output voltage cranking it.
I checked and cleaned and put anti-oxidant paste on all battery, ground, and power connections. no improvement.
I brought it to the Ashland VA Bass Pro Shop for a computer diagnostic. Morgan took one look at it and asked why I was using Autolite iridium spark plugs? (Advance Auto said to... duh?)
After checking it out, he changed out the plugs with NGK and it purred like a kitten.
That was the final fix, new NGK plugs. yes there was the bad coil and diaphragm along the way, and who knows what else I fixed. But the final lesson is that the Optimax will not idle unless you have NGK plugs. There is reportedly a resistance difference, and the spark won't jump the gap if the Autolite is used.
Thanks again for all the help, I hope this post serves to list the many possible (too many?) ways an Optimax can not idle. Good Grief (Charlie Brown).