I'm working on a Coleman UTV 400 that has a rough idle, owner has had it for about a year. When I say it has a rough idle, it doesn't have the continuous smooth running sound. At times you can hear it kinda skip, sputter, or like the RPM has fallen (RPM stay constant according to the gauge) It's not as bad as it was after I replaced the fuel filter and fuel injector (both are Chiki) not sure if that is a quality brand at this point. Checked the spark plug, it was a little foul, but not too bad. (Since the engine is still idling bad I'm going to replace that) Cleaned the throttle body making sure the carbon and soot has been removed, and the air-filter has been cleaned. New fuel is being used so it's not old or been standing. They did tell me that they were using non-ethanol fuel, not sure if that would be causing the issue. Next two things I can think of that maybe the issue is the O2 sensor or the valves need adjusting.
Thoughts and suggestions? Thanks in advance.
