2020 UT400 surging after sitting for winter

[jugliner]

I have a fuel injected UT400 that will start and idle, but surges and sputters at higher speed.  It has been sitting for 2-3 months and was fine when parked in garage.  I assumed it was a fuel/air problem and pulled the throttle body and cleaned it up.  I've ended up replacing the injector, IAC valve, MAF Temp Pressure Sensor, and fuel filter.  I've also checked the spark plug, Still surging.  I reset the ECU after every component swap.

I plan to pull the throttle body again and look evrything over for any visible leaks, etc.

 

Any suggestions would be appreciated on next steps.   The problem developing after sitting makes me think it should be something simple, but I'm stumped.  BTW the fuel was fresh and treated with Stabil.

 

Thanks.

[Jaygyver]

I would check to make sure the fuel line is not partially plugged also. Ether at the tank or in the line. Maybe blow some air from the filter back to the tank? I don't know if some of the brands have a screen filter in the tank.

 With fuel injection it has to have a pump so maybe check that also? And no I Have no idea on a small air cooled engine where or what it uses, lol. If you haven't already done a search here there should be a few of the same problems on other brands that either use the same motor or is similar in issues.

 You might want to go to Coleman's website and see if you can download the manuals and such to get a better idea on what to look for. Check which motor you have now as company's change out motors often either for better deals or having issues. I downloaded everything from my company, engine, axle, transmission, etc, I may not tear it apart but I can at least narrow down any issues I may have.

 

 You're going to get A LOT of other recommendations, I use the Sta-Bil -Storage- version year round as one year I may only use 10 gallons then the next I may use 40+ gallons. I also use a gas station that is fairly busy as then the gas is a lot fresher than a mom and pops off the beaten path. I've used it for the last 20 plus years on everything gas, chain saws, pressure washers, mowers, generators, etc. I have 4-14 gal tanks, 2 for gas and 2 for diesel. I just don't use enough fuel in one year to justify a larger tank and this way as one empties I have the other one to use and can then go into town the next time and fuel it up. For ME I've had zero problems with it.

 

[jugliner]

Thanks for the suggestion.  I should be able to get back to the UTV in the next couple of days.  Checking the fuel supply is next.

[jugliner]

On 2/17/2026 at 7:59 AM, jugliner said:

Thanks for the suggestion.  I should be able to get back to the UTV in the next couple of days.  Checking the fuel supply is next.

Fuel supply if fine.  Pressure is holding after fuel pump turns off.  Pressure is fairly constance when the engine is running (roughly).  I'm beginning to think I'm not getting enough air mixture.  I get the smell of un-burnt fuel.

[Jaygyver]

 You know it's sounding a bit like bad gas also , if you haven't already my one other last try would be to make sure you have good gas, wouldn't hurt to drain the old gas and put in fresh new gas. Gas stations have been known to get some bad gas sometimes and doesn't really bother cars as they have 15+ gallons to mix it with and they use it up fairly quick so usually don't even know it. Make sure you get the gas from a busy gas station as they will have the freshest gas just because of the traffic. Gas sitting for 3 months shouldn't normally be a problem. 

As far as Ethanol gas I have use it in all my equipment from day one and have had no issues related to it in any of them. I've only use a gas treatment (StaBIl-Storage) maybe the last 15+ years but never had problems before but decided to not take the chance and started using it.

My only suggestion now would be to do a search for "surging engine" or the like and see if you can narrow it down. There are other makes that have similar problems with different engines but they all run the same. Unfortunately this forum seems to be a hit or miss with help, people having jobs, or busy life in general so keep trying.

 Sorry I can't help more but if you do get it going please repost here on what you did so others can see it.