I have a stihl ms200t that revs up fine but want idle ?

I thought it might be the carb but I took it off and put it on another saw and it idled and ran perfect . I put the carb back on , fired it up and took a can of starting fluid and sprayed it on the crank seals wile it was running to see if it would change the running. It didn't change I tried my best to spray the impulse hose and intake and still no change . I am at a loss could it be a coil?