The engine misfire would make it vibrate at certain RPMs especially near its resonant frequency.
The other thing that may be wrong, especially with a transverse mounted motor and all that horepower, are the engine mounts. They go bad pretty quick especially if you drive the car hard. You can check this by starting the car and putting the parking brake on. Open the hood so you can see the engine as you are going to watch for excessive movement, more than a few inches of travel at the most. Should be very little and return to postition quickly. Then, put in first and give it a little bit of quick gas and clutch while watching the motor. If it moves as though it had nothing to damp or control the motion from torque and/or it moves more than an inch or so, the motor mounts are probably shot. The thing about replacing mounts is that the front one fails first in most cases. Some people replace just the front and the other mounts like the back mount are near failing and the load is transfered to the new front mount and it gets detroyed. So, you have to replace the motor mounts as a set and it is a good idea to replace the transmssion mount as well. If you want to get some longer lasting mounts or strengthen a stock set to prevent or at least lengthen the time it will take before they fail, you can get polyeurethane mounts or inserts. The mounts are sold in sets and will keep the engnine form moving around better than stock meaning better power transfer. The 2 places I would suggest getting mounts are innovativemounts. Com or hasport. Com. They will last the life of your car. Get the standard shore grade as anything else will be too rough. The other option is to get a set of new stock mounts, or you may be able to salvage your old mounts depending on how bad they are, and buy some inserts from Energysuspension. Com. They will have a full kit for all mounts for much less than getting the hasport or innovative mounts. They will be a little harder than stock but still retain some of the vibration isolating qualities that stock mounts have.
So, get the misfire straightened out and then if it still vibrates check the motor mounts.
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Sunday, January 22nd, 2012 AT 10:05 PM