2002 Mercury Marquis

My car seems to vibrate at different speeds. Its not tires because its a quick vibration or shaking. At first I thought it was just the road. I had the rear axels replaced and shortly after that I started noticing a vibration that felt like the road was a washboard. I did not think nothing of it then it started happening more. It feels just like you run over a washboard road for a split second sometimes longer. I would turn around and go back over the same spot to see if it was the road and I could not make it do it. My coils are going bad but that is a miss not a vibration. Any know problem with these cars that cause this.
February 1, 2007.

Would you call it a shudder? Is it more consistent at the same speed or gear shifting point?

Well you might call it a shudder. Feels more like I ride over a wash board. It does not have anything to do with shifting, it is not at a shift point. It happens at different speeds. However Higher speeds are more agressive wash board feel. Today I noticed more coughing of the bad coils and feel that might have something to do with it. But again its like driving over a bunch of ripples in the road. Like the ripples to warn you you are going off the road.

Feb 2, 2007.
I think the starting point on this is to retreive the codes from the computer to start narrowing it down.

Well took it to the dealer today and no codes listed but after driving it I had two problems. One number 6 coil bad and transmission converter going bad.

Feb 3, 2007.
That was why I asked about the shudder, there is a tsb on the converter for that. Glad to hear your success.