I had headers installed a few weeks ago. Then I started getting this vibration in the gas pedal at 2700rpm. I pulled the pass wheel off and the black plastic piece in the wheel well, and tightened all of the bolts I could get at. The vibration went away. Then it came back after a few weeks. Check the bolts again some are loose again. Tighten them down, and one of them started to strip. Still have the vibration just not as bad now. Are there any bolts out there that will not loosen with expanding and contacting for the heat from the headers.