...it came off while I was under the car poking around, located somewhere between the radiator and the engine block. Both of them are in bad shape due to some front-end damage some years ago. Are they important? Should they be replaced? The one on the passenger side has a cable/wire fastened to it so I'm likely to leave it alone. I'm also planning on replacing the wheel-well liners. I'd like to just rip' 'em off because they're both kind of mangled, but I don't know if it's alright to drive for long with out them. Thoughts?
Looks like one of your under engine splash shields. Yes I would put it back on or buy new ones. They protect the engine and wiring from too much water and dirt, plus they add mpg due to less air drag on the car. Some aftermarket versions are pretty cheap but usually they just need the clips.
I'd check prices before pulling them out, if possible, suspect refurb' is preferable to buying new ones wherever possible, they can be pricey.
