HELP!! Is anyone familiar with this problem?
 

I have 97 e320 88000 miles. Computer codes given out are 133 and 140, both related to 02 sensors. Replaced them with new. With scanner I can see the o2 sensors are working fine then suddenly they lose signal and will set codes and check engine electronics lights. Sensors are in proper working order I just don't know where else to look, any insight on this???