OK so would the gas being 2 octane diffrent really hurt anything. i mean last week, my car was running bad, and had a missfire. so before i knew it was a missfire and changed my wires, i went and put unleaded plus in my car, now i am just running unleaded because my car is running good again. but my fuel economy has dropeed big time. i mean even driving her harder after i fixed the wires, i still got 125 miles out of a half tank, now taking it easy alot i have only gotton 90 miles to a half tank, would the diff octane do that??

 

nope... you should pull one of your forward o2 sensors and see if it's caked with black crud.