Worn steering parts, worn suspension parts, tires out of balance, out of alignment,
try new tires and a front end aiighnment.
Front shocks. You may feel what I could describe as an "UP" bounce feel. If you replace the front shocks this will minimize that feel. However, the Frontier front suspension is quite "bouncy" good truck.
A 1994 Corolla engine may vibrate if the motor mounts need to be replaced. The motor mounts can be purchased at any auto parts store.
Check your front bumper, it might be loose, or the radiator fan might me hitting the case, or all your nuts are loose and its about to fall appart :P Could use more info like when does it vibrate, at a stop, driving along slow, driving along fast or braking.
Warped rotors is the most likely cause. Have the rotors turned or replaced and new pads installed.
Possibly a bad wheel bearing.
Bad axel shaft u-joints. U-joints bad in the front driveshaft. It would really help to know the year.
You might need an alignment.
You are driving over the 'cats eyes' marking the lane boundries.
Unbalanced front wheel.
Probably bad shocks.
Check the front brake pads.