I have a 1990 acura integra rs with 200,000 miles on it, and i am getting really bad gas mileage now along with a lot of black chalky substance on the exhaust pipes and back of the car. Just wondering what it could be possibly bad o2 sensors or what? I already have had all the carbons cleaned out of the top end of the engine.

 

black sooty stuff usually means you are running mad rich. you can also check your spark plugs as a good indicator. black - rich. yes bad o2 sensor can make you run rich. do a tune up and replace the o2 if it's never been replaced. make sure you reset the ecu after youve done all this.