Hello. I recently purchased a 1999 Civic HX after losing my CX when someone pulled out in front of me. I averaged 38mpg with the CX. I commute about 70 miles a day, 90% is highway. A/C on 50% of the time. Averaging 70mph. I'm averaging 32mpg after 5 tanks of gas in the HX. It has a manual trans, 217,000mi (30k on rebuilt motor) and steel wheels. First thing I did after buying it was get an oil change. I haven't done anything else yet other than new shocks/struts and tires.
What should I be looking for in trying to improve my numbers?
Inflate tires to max sidewall rating
Jack up each wheel and spin it to be sure that a brake isn't dragging.
See if there are any stored codes on your ECU related to the oxygen sensor.