Vibration problem on my Explorer

Explorer 94 I have vibration problem when i accelerat above the second and very stronger at gear five, and when my speed is reach the vibration drop but not stop completly, i check my tire and my drive shaft ,and no damage I do test with my engine, i disconnect the computer advance signal because i suspect the timming advance on my engine, and i notice when i running, the vibration get better but not stop i do code test and i have code 335 (engine stop, key on) and 336 (engine runnig) that mean EGR circuit problem but, i dont thing is the problem about the code do you know what i need to change and if is the cause of my vibration problem