I just bought a 2003 A4. It has the 3.0 manual trans quattro, and 90,000 miles. I had driven it very little before I decided to do some maintenance. I changed the spark plugs, and replaced one of the valve cover gaskets that was leaking. I went to start it up afterwards and the engine has a very distinct vibration. It causes the whole car to shake a little bit. The Check engine light has not come on, and I am getting no codes. I thought it was the coil packs, so I bought three brand new ones. I put them on one side, not any better. I took the three that I had just taken off and put them on the opposite side, and it still does the same thing. I'm out of ideas, and am new to audis so any ideas or comments would be greatly appreciated.