over the last week the sapph started running a little rough,idle wasnt as smooth and occasionaly on boost it would splutter.

the car is stg3 runninga msd closed loop chip.whilst trying to sort the problem out i was messing with the lambda sensor and once i unplugged one of the pins(black one) it drives alot better,the senosors only a few months old could it be shot?why would it work better with it unplugged??

any help appreciated.