o2 sensor would clog causing the air to fuel mixture to go to hell ... the bad part is o2 sensor going bad through burning out naturally over time is not as bad cause it naturally skews the reading to a lean mixture (voltage skews downward) so the car just runs rich till you fix it... but with a clogged up sensor its voltage readings are not skewed and it sees less o2 flow so it actually leans the mixture out... so yea, you can blow the engine up if it clogs up bad and you do not replace it in time...