What is wrong with my car? It shakes when I start it.?

umm...... Take it back to honda right away you have a very bad engine! Make them fix it!

There is an anti-puff back valve in the exhaust system that has likely failed. It maintains back pressure and prevents the exhaust from puffing like that. When it's bad, the check engine light will turn on due to the lost compression. Have your dealer replace it

Replacing the engine block is a big, complicated job. I'd guess they forgot to hook something back up when putting everything back together. I wouldn't be too dang concerned about something being ruined, but definitely get it back to them as soon as you can (try not to drive it anywhere else if you have another car you can use in the meantime), because a small problem can cause a bigger one if not fixed promptly.

Before you drive it anywhere, call up the dealership. They may prefer to tow the car back to their shop (at their cost), rather than risk more damage happening to the car that they have to pay for as it's driven to the shop.

take it back to honda. its under warranty . even if they have a lot of idiots working in their shops they have some qualified mechanics

Motor Mounts ???