Good advice.. I had to lift the mower up with the tractor and a chain to look if there was a stick wedged. I will remember to remove the spark plug next time I'm under there. I don't know anything about the other so will have to have the smoke screen . Lol. I know my mower blades could stand to be sharpened but that's beyond my skills.:-(<quoted text>
Typically, the shaking in a lawn mower has nothing to do with idlers, but more often a bent blade. Check your blade. It can sometimes be taken off and straightened and resharpened, but easier to just buy a new one for about $15. You can take the old blade with you to get the correct match for the mower.
Next mechanical guy that comes along ...lol