boostedsi99

hey i have a 99 civic...i have my 2nd 02 just hanging on my exhaust it's not in my piping i have no check engine but when i just crusing i see my a/f guage and when it goes to lean my car pull back pulll and then pulls normal as soon it goes to rich...someone told me b/c of my 2nd o2 reading wrong...but i have change my first o2 and it does the same..and yes a/f is coneected to my primary o2..if anyone can help...thanks