p2161 p0170 p2187

I'm buying this gen coupe with 148k miles and these fault codes popped up Ive been reading around and everyone mentions an o2 sensor. the mods done to this car are very vague and I don't see any brands on it, all I know that it has no muffler, it has an aftermarket air intake, and aftermarket blowoff valve. I want to know what I do from here because the care feels sluggish.