so unfortunatly my last oil change consisted of poonzoil, and ever since a recent issue with fuel pressure and a broken vac line (which was resolved) ive been running rich and throwing an o2 sensor code. (and i changed both o2 sensors) but still drives very well...just can tell its bogged down and not burning all the gas. but now its gone a little further as a friend said he saw a tiny bit of blue smoke when i drove past him today. regardless of how im going to solve this issue...first thing is the oil needs to be changed. but after reading some good reviews about seafoam im going to give it a shot before i do. and possible some lucas oil injector cleaner as well? (my engines at 150k now)..so im going to remove my cat as its fairly new, and put a 2' long pipe i have lying around in its place while i run through the seafoam. what id like to know is if there is anything i can do to avoid the possible distruction of my new upstream o2 sensor?...i know i can take out the downstream without much effects for a 5 min drive but what about the upper one? my wallet says i should avoid the chance that it could be ruined. im expecting there will be a good bit of build up as well by the way (slightly heavy foot, horrible oil thats been in too long AND high mileage couldnt have added up well) stupid.