what is a MB booster?

it occured to me to check the 02 sensor. I keep a book of every gas fill up I have ever put in my car. last two fillups are 22 and 23 mpg.

some more info on my situation.. my poor gas mileage happened almost immediately after I replaced my ignition coil, cap rotor and plugs. Like I said they use to be.060 inches and now the new plugs are at .040 (factory)

I was going to check for any codes the car might throw....asiandood, how do I get to that two prong connector? i looked and looked but I couldn't find it?

what SHOULD the residue on the o2 sensor look like when I remove it?