Does sound like a motor mount. Check to see if the nut is still on the bottom in the k member or see if the bolts are still in the block holding the motor mount. If they are still there you may have a torn motor mount.
Kind of easy to change out if you have an engine hoist to hold the motor up.
90 LX hatchback
(sold but not forgotten)
89 LX Notchback
No motor/trans (for now)