My 05 Vector ran fine a month or two ago. Today I start it to go for a quick spin and it won't run well except at idle. If I try to ride it, it farts and carries on then the check engine light comes on. If I then let it go back to idle, the light goes out. It seems to be running on 2 cyl.. A plug check shows all the same. If I run on a jack stand the engine light does not come on but it is noticeably down on power. Any ideas ? Thanx