2004 Pontiac Grand Am Shaking

Recently my Service Engine Soon light came on and the car started shaking while in Idle and would have some shaking going on when starting to speed or going over 45 to gain speed.

Now I've changed the spark plugs & the spark wires and added some Fuel System cleaner. At first the Spark plug / wire change did not help but the Fuel system cleaner turned off the SES light pretty much right away.

When the next day I started it, the SES light blinked for a little bit only to turn off than I drove it for about 60 Miles and didn't have any problems (no blinking SES light or steady on light)

Now last night it blinked a little bit on me twice and it would jerk a little bit when trying to gain speed (over 45 MPH) as I would let the gas go and push it back it would go away.

than today I am back to square one and the shaking is back the way it was. I got a nice unclear code (p0300) when reading it. And it blinked on me once when trying to gain speed again. Also once I maintain speed the light just stays solid and doesnt blink again only when I try to gain it after 40 MPH and than it's only once not multiple times