so i replaced passenger side sensor back in oct. everything works great and i even cleaned the Tb a bit. lately my cars idle has been fluctuating between 600-700 rpm and shaking a bit like it wants to stall. is this wat happens when a sensor is going bad? i have no codes but a gut feeling maybe the driver side is going since the passenger side failed a few months ago. are these normally replaced in pairs? id hate for the driver side to fail and i dont have a replacment sensor. should i jus buy one jus incase?