curious anyone know for sure if 95 thunderbirdLX 4.6 has 3 or 4 o2 sensors on my car front 2 are smaller which would be upstream at cat next 2 are larger and are in the pipe next to the tranny both sides went to advance auto they say my car only has two upstream go figure whats the deal having issues with car idling below 1000 rpm at idle and thinking maybe after running a diagnostic on computer said may be 02 sensors ,i did remove mufflers and used two tail pipes after resonator wondering if computer is sensing less back pressure and trying to compensate for it i know my check engine light has come on and gone off several times over the last couple months and o2 sensors are all factory never changed as far as i know with 116000 on car hmmmmm help