As I was driving, the steering wheel started vibrating, I tried to step on the gas pedal, but the car was not accelarating. After a few seconds, a tar-like burning smell was coming from the driver side. Could this be a spark plug or motor problem? Is it one of the calipers? Please help

 

The left front caliper could be "HUNG UP" causing the brake pads not to fully release. This will cause excessive heat and will lead to the rotor warping (the vibration) and the bearing grease frying out of the hub assembly (the tar like smell). Need to have the caliper, rotor ans hub assembly checked.