Q: Engine shakes upon startup.

I can be quite alarming to start your car and have the engine start loudly shaking. There are a number of reasons why your Ford Focus is experiencing these symptoms. I have seen a number of shaky engines due to bad engine mounts. Engine mounts keep the engine firmly in place and reduce the vibrations in the car for a more comfortable ride. Another reason for shaky engines are engine misfires. If you are misfiring then your Focus may be due for a tune up. I have also seen shaky loud engines being caused by bad timing belts. When a timing belt is brittle and worn out, it will jump tooth, meaning it literally will grab the next tooth on the belt zipper. A timing belt jumping a tooth will change the timing of the engine and it will not run correctly. For all of these possibilities, it is best to enlist the help of a certified mechanic to inspect the shaking and get your Focus back to running great during start up.