My '90 LX 5 speed has developed a vibration in the driveline. One day it was fine, the next it started. The vibration gets worse with speed. It starts to become noticable at 25 and becomes progressively worse as speed increases. It does it in every gear, even if the transmission is pulled into neutral and the car left to coast. These things had me thinking wheel balance, EXCEPT the vibration goes away whenever the throttle is applied. A little throttle or alot, and no vibes. As soon as I back off the throttle, the vibes return. So it vibrates on decel, throttle off cruising and tranny-in-neutral coasting. Any ideas? The car has been driven easy (nothing over 3000 rpms and no overly hard driving) as the motor is still in the break-in period (under 300 miles). Thanks.