whats the easiest way to remove it? its a tight fit, thanks

 

jackstands and a O2 sensor socket. lots of PB blaster, too. if you can get access to a pit like at an oil change place or if you can get the car up on a lift that would help you TONS.

 

^Might I add some heat! Either from a torch, or just go out for a good ride and come back and do it quick.

 

PB Blaster, WD-40, Kroil, etc. is a good start. Some type of lubricant, because that sucker is no doubt rusted good.

An O2 sensor socket is nice, but I've actually broken them on Lancer O2 sensors... Nothing beats a Big F***ing Wrench. A large Crescent wrench works well in this case.