shaking in the car

every time i step on the gas in my 97 ford mustang, it starts to shake. it shakes few a few seconds and then stops. im not really sure why or what is making it do that. help pls

Transmission question; is yours an automatic or manual? Also does it only happen while driving, or does it happen when you rev the engine while parked too?

its automatic and only happens when im driving. its like as soon as i come to a stop, and i push on the gas, that's when it starts to shake and then it goes away