2000 Civic / Poor city milage / Great highway mileage

My civic has always gotten around 28/city and 35/hwy, About two years ago, my city mileage dropped to 18. Highway remained around 35. My mechanic changed the fuel pump and oxygen sensor, neither of which helped. Then he discovered a small hole in the vacuum advance hose and replaced it. The mileage shot right back up to 28. It stayed there for several weeks, then dropped back down to 18. He can’t find anything else wrong with it. Told me the car is getting old and things loosen up. That would make sense, but it seems odd to me that my highway mileage remains at 35. Any ideas for poor city but great highway mileage? Thanks!

A number of things could cause a drop in fuel mileage but there’s not enough information known to really narrow any guesswork down.

However; a fuel pump is not even going to cause this kind of problem and if there’s nothing lost in translation I might add that your car does not even have a vacuum advance or a hose to connect to it. Vacuum advances are up there with dodo birds on the extinct list.

Any slightly rough idle or hesistation, any Check Engine Light on at any time, car been scanned for codes, etc?

Ya fixed it once… Somebody should check to see if the vacuum advance is working. The distributor cap has to come off and the pickup has to move when vacuum is applied. Sometimes the arm has to be bent a little or it needs a little grease at the pivot. Now that you have full vacuum the diaphragm has probably ruptured.

I don’t believe your car has vacuum advance so maybe you meant vacuum hose. If so then I don’t know.