After driving a short distance the front left brake will start pulsating causing a heavy vibration. Most times it starts only when over 65 mph. Sometimes it will stop without reason. There are no dash lights on. When I stop the car the rotors are extremely hot when compared to the other brakes.
I've done the following with no improvement: changed speed sensor; rotated and balanced the tires; changed the ABS fuse; operated the car without the ABS fuse.

The only thing my mechanic found was the rear left speed sensor was bad and was replaced.

Is it the caliper or something electronic?

Thanks for any input.