My g/f's car (2003 Olds Alero 2.2) has had an O2 code for about 2 weeks. She says it runs bad and it does seem to. The code was for upstream oxygen sensor. So I replaced the sensor with a new Delphi and cleared the code. Well it comes back so I tell her next time fill up somewhere else rather than her usual spot. This was several days ago and the code hasn't cleared itself. Tomorrow I am going to double check and make sure the sensor is tight and put some dielectric grease in the connector. Also probably get the battery tested just to make sure everything is getting power. Pretty sure that won't do it so I've got air filter, fuel filter, and plugs planned. I've got an OBD2 cable for my laptop on the way cuz I'm thinking I'll have to have it on a scanner to see what's up. I'm kinda thinking it might be coolant temp sensor bad or something. Am I missing anything?