... the oxygen sensor?? My husband has been all up underneath our '91 Audi 100 5 cyl and for the life of him he cannot find it!! Can anyon eget me in the general direction?

 

i think its the same for my 5 cyl.. Jack up the pass. side of car... take off wheel. There should be 2 holes in the inner fender when you look directly where the tire used to be. Your oxy sensor should be in the down pipe or by the cat. converter. Mine was in the down pipe. It is kind of hard to see (and kind of hard to stick your hands into the holes to replace it). IMPORTANT.!!!! To save yourself some trouble.. when you find the 2 wires that connect from the oxy sensor to the drivers side of the block (they are kind of by the radiator hose) unplug them (remeber to disconnect battery) and tie a string around both of them (twine will do and make sure you have it long enough.. leave enough hanging out the front of the car in case)... so when you take your oxy sensor out from below.. you will get the wires and string too (there are 2 or so wire stays that are clipped on they may or may not come off with your old wires but be sure to put them back).. so when you put your new one in.. tie the string to the new wires.. and pull the string from the front of the car to guide the wires back up where they were. Then put the oxy sensor in. .. remember to put anti seize stuff on the threads!

I hope you can spot it, its usually brass in color. If you still cant find it, i can try to take picts of where it should be (on my car). So i hope this helps!