Any ideas what this could be??

[blue62]

Originally Posted by Chboro

I'm the second owner. Had no maintenance records when I purchased 7 years ago. I'm thinking the mounts are all original. When I replaced the plugs and tubes I did examine the coil packs and all were good. First time I ever experienced this vibration at any speed. When it happened I was going a steady 82mph. No excessive play at the shifter. I'll look at getting the tranny and engine mounts replaced 1st.

The tranny mounts are oil filled so if they are not leaking oil they are most likely fine.
The center mount (engine mount) on the other hand has a rubber center that is certainly shot after 20 years.
If it is shot and you are in tune with your car you can feel the engine rotate in a front to back or back to front manner when slowly letting the clutch out. The shift lever will sometimes move in a forward to back manner as well.But not always.

Or if you slowly go over a speed bump you can feel the play in the mount, sort of a slight forward to back rock of the engine. Sometimes a little clunk or thump.

As for your vibration at speed check the bolts that mount the drive axles to the trans for tightness. Six per side I think.

I had a similar thing happen but at around 75 MPH but I could feel it in the steering wheel.
All new Michelin P4 tires.
Took road-force balancing the tires to sort it out. Regular balance method didn't cut it.