Your engine is not failing. This is a sign that there is A. Junk in the blower motor causing it to be off-balance, or B. the motor itself is starting to go bad and is allowing the squirrel cage to flop a bit and vibrate. Let me guess, you can feel it in the pedals when its on 5 and vibrating, right?
As far as your car vibrating more than it should at idle, when was the last time a tune-up and vac. leak check was done? I'd start there before anything.