Google "spark plugs blow out on 98 toyota tacoma" and you may get a hit. If the plugs were so overtightened that the threads are stripped you may be able to repair it with a heli-coil. If they are just working loose and are correctly torqued you have a serious problem that is not going to be an inexpensive fix. Check with your Toyota dealer to see if there have been any recalls for this problem also. Toyota is very good about fixing unusual problems provided the vehicle has been properly maintained. You have an unusual problem. Good luck with it.
