Most commonly a vibration while driving is from a broken belt in one of the tires, but if it's vibrating while sitting still, it's usually from loose motor mounts and/ or a higher than necessary rpm
inside the gas tank
700 RPM
Maybe on the passenger side near the firewall
Check firing order
It should be behind the glove box in an access panel.
On the transmission under the shifter cable bracket
1-6-5-4-3-2
Old age Frozen or misaligned pulley
could be blown fuse or short in wiring
Where is the thermostat located on a 1987 Buick LeSabre?
On Second Avenue was created in 1987.
A bad head gasket or a cracked head can do that.