Help Plz.

[Goat]

i don't know so much about cars, but yeah:

A few days ago my is300 had the little light up that said engine check or w/e. So we took it to this dude and he said an oxygen like cord thing came loose, and was easy to fix, cuz he only charged like 15 bucks. So after the fix, my car was running fine again until yesterday the light popped up again. I also noticed my car is slower and takes longer to get going like it did before we got it fixed. I'm almost positive it's the same problem as before. I was just wondering if anyone had a clue what I'm talking about, and if i could fix it myself. I don't really know how to describe it except it's some wire thing that gets oxygen (yes im dumb). Thanks.

edit: nvm i need a new part :(