Hi everyone, I have myself about a 2 week old cobalt 2.4 (new). It had a vibration when i got it. I thought it would go away after it breaks in and the tires even out. After 1200 miles it never did. Anyhow one day I decided to check my tire pressure for kicks (they didn't visibly appear low) I was shocked when the gauge read 25 psi. I was suspicious so I used another gauge and it gave me the same reading. Anyhow all 4 tires were 25 psi, sorry one was 27psi. i pumped them up to there 35psi as stated in the door jam and what do you know, vibration 90% gone. accelerates faster, rides smoother, and mileage went from average 27 to 30. who would of thought the dealer doesn't check tires before delivering a vehicle. I thought they had to check tire pressure when the inspect the vehicle. Anyhow some tidbits if your having vibration issues. It just might be even simpler then an out of balance tire.