My car is shaking at speeds at 45mph or higher. I know it's not the tires cause I got it balanced. It almost feels like my motor is causing the shaking at high speeds. The shaking/vibration almost feels like a tire being out of balance. That is why I got the tires balanced first. What I need help with is: Can a seized spark plug (cylinder #1) cause this trembling? Also can it be due to suspension, my shocks are currently dead (6 year old tokico blue) and my springs are also 6 years old (eibach springs, I can't remember but may be the sport line)? Currently running on a stock SOHC motor. Any help would be greatly appreciated.

 

Is the shaking in the steering wheel or in the car only?

 

Car only. Yesterday I was driving at around 55mph on a smooth stretch of road with no shaking at all. All of a sudden i hit a small pot hole and my car started to shake really bad until I got it under 45mph.

 

Sounds like it's definitely in the suspension then. Another thing that will cause a shaking (on acceleration) is bad inner cv joints, but if it's at a steady speed then it's probably in the suspension. You stated that your shocks are done, well yeah that'll cause shaking. There's nothing to stabilize the springs and reduce the oscillation. So yeah, you hit the smallest of things and the tire will bounce for half a mile down the road. I'd start there since you know they are bad. Then move on to the next worn out item...

 

jack it up and spin each wheel see if there is any wobble.