One problem related to emission control has been reported for the 1998 Mercury Mystique. The most recently reported issues are listed below.
Oxygen sensor keeps shorting out. Oxygen sensor has been changed 5 times. This is 6th time taking it back for same thing. Dealer can't find problem. Computer just reads that it's bad. Consumer states oxygen sensor has now been replaced eight times, the dealer is only changing the sensor, the problem is reoccuring and needs to be resolved by finding the root of the cause of the failure, the engine lights keeps coming on.