[s-cars] I want my MPG

[Floyd Noel]

Listers,
My s-car has been getting horrible mileage lately (around 11.5) and I  
have been trying to diagnose the problem. Power seems like it has gone  
down as well, but my butt dyno isn't the most accurate, and it still  
has way more than my work Malibu. It also seems like to me that there  
is more smoke coming from the tailpipe than I would prefer on cold  
mornings, but in the daytime it is not really a problem. I just  
replaced the spark plugs recently, not much difference.   From the  
research I've done, it seems like it might be the oxygen sensor, and  
I'm not sure when the last time it was changed, so I figured it  
wouldn't hurt to change it. Are there any other things I should  
consider or steps I should take? I bought fuel injector cleaner as  
well but haven't used it yet.
TIA

R/S
Floyd Noel
Sgt/USMC