Well if the clutch is in and it even does it at a standstill with the engine revving, it's engine and not drivetrain.
The harmonic balancer is the very bottom pulley connected to the crankshaft, it is the pulley that has the timing marks on it. These do sometimes go bad. I have replaced mine with a Fluidamper when I had a bad vibration once, but it turned out to be the flywheel instead. The balancer is actually pretty expensive. I believe (it was a long time ago...) mine was like 375.00 from Summit.
Good luck, and I hope you find the vibration. I am dealing with a bad vibration in my car now that I believe might be the driveshaft, but am not sure, and it's driving me nuts, so I know how you feel!!!
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Joe!
1988 GT, 167,000 miles!!! 13.71@105mph Check out my listing!
Click here! Or my website:
www.joe4speed.com
1999 Ninja ZX-6R 10.32@135mph!
1993 Olds Eighty Eight LSS