after changing my 19lb injectors out back to some 36lb injectors, i forgot to change my injector constant and the car was running extremely rich, i assume around an 8:1 ratio? i ran the car idle for about a minute and drove it around the block for maybe 2 minutes before i realized i forgot to change the constant, now that its changed and everything is good, i have been getting worse gas mileage. my question is... is it possible that the 3 minutes that i ran the car that rich have ruined the O2 sensor? its only got maybe 500 miles on it. and my tune was good on the 36lb'rs before.

Possible, but methinks unlikely. More likely, it sooted up. Whether or not you can safely clean them, I know not. If it is sooted up, likely you'll know that immediately when you take it out and look.