2006 Ford Focus Check Engine Light

Hi, My check engine light is on, comes and goes but is more on than off. When accelerating whilst driving, the gas pedal becomes very stiff and my car does not gain speed, teh rpm dial does not seem to move. It struggles to get past 40mph. Alos, whilst stationary at a traffic light in neutral, the car vibrates heavily, feels like it is going to cut out. This sometimes also happens while driving.