#3 cylender mis firing..why

I recently brought my car to aamco because it was bucking and the O/D lighti was blinking. They told me that it was a motion sensor and they are repairing it, but they also told me that my #3 cylender is misfiring, why would it do that? I have 191898 miles on the 96 explorer, I recently changed oils and bought that high milage oil could that be the reason??? Help please, and until I get it fixed is it ok to drive the car??

Chances are a fouled plug. And don't say you recently got new ones. I've had these fail in my Explorer in less than 4K. One problem is cracking on the insulator just under the boot. A result of lack of insulating boot grease. The other is a slight coolant leak from lower intake manifold that fouls the electrode insulator.