2014 Mercury 60hp 4S surging when going back to idle after running wide open

[Harleyscooter]

2014 60hp ser no. 1C264376 model 1A60413B2 the motor was originally purchased in early 2015 on a Bass Tracker 175 TXW, I bought it in the fall of 2015. It has very low hours. I drained all the fuel I could last fall, this spring I put 11 gals. of REC 90 in it. When I started it at home it ran fine but under load it would surge in gear from idle to about 3k rpms and it got worse the more I ran it. I added a can of Seafoam and it helped some then I added a bottle of Lucas injector cleaner and changed the plugs after running the full rpm range. Now it runs good (33mph @ 5900rpm) until you come back to idle and the it surges until you speed up a little, one time while surging at idle in gear I pumped up the primer bulb and it ran good until the next time I came back to idle from full throttle it would surge I pumped the bulb again with not much improvement. I then changed the low pressure fuel filter, The filter would only fill with about a 1/4" of fuel when running on the hose, is that normal? I have not had it out again, but the filter I removed looked good. THE MOTOR DID SIT FOR ABOUT 9 MONTHS after last years winterization. Any thoughts would be greatly appreciated.
Thanks

[Harleyscooter]

I went to a dealership and talked with a mechanic today, his opinion was that there is water in the system from sitting for 9 months, and I should drain the tank and the VST leaving the plug out overnight to get any water moisture removed, also drain the filter I just put on and replace the Hi pressure filter, Add fresh REC90 fuel and see if that fixes it. I will see if there is any noticeable water in samples from the tank and VST tank.

[EuropeanAM]

Agree fresh fuel is a good starting point, but use the fuel the engine was DESIGNED for: 87 Octane, with no more than 10% ethanol content.

Then see how it runs- IF there are still concerns, there may be some relatively simple solutions.

[Harleyscooter]

Thanks for the reply, I did check 5 separate qts of fuel from the first filter fill hose and drained the VST a couple of times and found no water at all in any of the samples? I am going to get a fuel pressure test kit today and see what the fuel pressure is in the VST fitting and to see what the pressure does when the engine stumbles. I will drain the rest of the rec90 out of the tank and replace it with some treated 87 octane fuel also. What should the fuel pressures be after the lift pump and at the VST fitting?

[EuropeanAM]

Lift pump: 3-6 psi.

Fuel Pressure: 42-44 psi.

[Harleyscooter]

Thanks for the info, results are 5 psi lift / 42-43 psi hi pressure at vst schrader valve. The pressure never changed even when the engine stumbled. I now do not think the problem is in the fuel system. With the plugs still running white after a few hours of run time, does the tps tell the computer how much fuel for the injection to send to the engine?

[EuropeanAM]

The TPS tells the PCM what the throttle position is. It is up to the PCM to match data from a variety of sensors to determine current or demanded conditions, and supply the correct amount of fuel (based on the data found in MAP tables within the PCM).

Plugs should not be running "dirty". White is not uncommon on 4-stroke models (even after a few hours).

Might need to get it on the Computer Diagnostic System to see what the IAC Duty Cycle is (potentially a throttle plate/TPS problem).

[Harleyscooter]

Thanks again for the help Don. I didn't want to leave the boat at a shop, the service dept. told me it would be two weeks before they could look at it. But I may not have a choice. I would not have a problem buying a TPS and putting it on if there is a "good chance" that is the problem. From looking at pictures of the TPS online it appears to be non-adjustable and just a plug in and go part? I have checked the plug wires, hoses and all electrical connections on the motor all seem good, I was looking for a vacuum leak maybe but I don't know if that would cause my problem or not.

[Harleyscooter]

Do we have O2 sensors in our fuel injection management system like cars? If so do they cause this type of problem? I'm just willing to try anything, my goal is to get the grandkids out fishing before they have to go back to school, the last thing I want is to take them fishing and have the motor stop running or hurt the engine. When the tech hooks up the computer to my engine will it tell us what the problem is even though it has never sounded any warning beeps since I have owned it.
Thanks again.

[EuropeanAM]

No- I suspect the problem is actually dirt/debris in the intake, OR an improperly set throttle plate (the later is likely the case).

DON'T attempt to alter this without the correct tools and a firm grasp on how the system reacts to even the smallest of adjustments.

NO O2 SENSORS in this Speed-Density system.

[Harleyscooter]

I went to another dealer and told him what it is doing and what I have done. He said that everything I have done is what they would do and the next step they would do is clean the injectors. After telling him I have never had a warning beep ever, he said hooking up to his computer would show nothing and do no good. I mixed 1 gal of new gas and a full can of sea foam unhooked the fuel line from the tank put the line in my 1 gal. can, ran them motor for 15 minutes waited 30 minutes did this 3 times (the last time I did it the motor would barely run) I reattached the fuel line to the tank let it sit for 4 hours ran it again 15 minutes then drained the VST it was clean. Now it runs good until you come back to idle and it stumbles. I found a manual online after looking at it I found a part called the IAC it says it is used to add air to the intake manifold when you come off of full throttle to eliminate the stumble of the throttle plate closing fast.

[EuropeanAM]

The IAC is the device used by the PCM to stabilize or adjust idle speed. However, it is an output, and is indirectly affected by other variables.

One of those (I suspect the one causing your problem) is the Throttle Plate Air Gap. Have seen a number of engines that were off either due to carbon/coking in the throttle plate, OR improperly adjusted throttle plate.

REQUIRES use of the G3 Computer Diagnostic System to accurately address this, and a working knowledge of how IAC Duty Cycle is calculated (as well as what changes occur with any adjustment).

AND it is a "learned" TPS setting- so engine must be shutdown and restarted after EVERY adjustment, then look at FRESH info to determine if any change occurred.

Moderately high-tech setup, some may not be familiar with it.

[Extremeboating]

This is exactly what I was looking for.

Every once in a blue moon, I get exactly what the OP described for his troubles at low speeds, but goes away when I give it more throttle.

I got the boat with less than 30 hours so I doubt it's a carbon issue. Probably a throttle adjust issue. At least I know where to go with it from here, as I have heard of other people having this issue with their Trackers as well.