Most likely its bad 02 sensor. I had a p0158 for 2 weeks every time I would shut it off it would come back on turned out bad 02 It came on right after I did a tune up so I thought it had something to do with that turned out just coincedence it could just b coincedence that it happened after the mil Eliminators. What I did was swapped the wires on the 02 sensors so bank 1 is reading the bank 2 sensor and bank 2 sensor is reading the bank 1 sensor if the code changes to the oppossite bank u found your problem its more then likely the 02 sensor. That's how I narrowed it down. But while I was down there I just replaced both it was worth it at only 48 bucks a piece.