Oxygen Sensor ?

I have a 1997 Merc Cougar 6 cyl that has 36000 miles - feels like it is
not getting correct air / fuel mixture - have to start it several times
to get past engine flooded or not getting enough gas feeling. Once its
running smoothly it seems to be fine but seems like its running
somewhat lean or rich ....can't tell which... is this an oxygen sensor
problem? Fuel filter, plugs, wires and all the rest have been done
recently. My friend tells me take it to auto zone - they do free
diagnostics and then will install the part they sold ya. Any help on
this would be greatly appreciated. Yeah it's really only got 36 K on
it....