Sudden decrease in gas mileage '97 civic
 

I love this car. Manual transmission, hatchback LX, 1997 owned continuously by me for almost 13 years now. It used to get about 33 mpg, driven mostly in the city. I had the timing belt service done a couple of months ago and since then, the gas mileage has decreased to about 25 mpg.

New front tires were put on the car at the same time, but I recently made sure that the pressures were good and the mileage has not rebounded.

There is no loss of power with acceleration (given the 100 hp, it's amazing the car can accelerate at all) and no obvious leakage of gas from under the car or any smell of gas vapor in the garage in the morning.

The dealership looked at the car and didn't find anything definitely wrong, but questioned one of the O2 sensors.

Anyone have any thoughts on the possible causes of this problem? Given the age of the car, I'm not thinking I want to spend a load of money fixing it, but if there could be something simple and stupid that I'm missing, I would love to hear it.

Thanks in advance.

jt

welcome to the forum. Spark plugs, wires, fuel filter, air filter, oil and filter, if the sensor is going bad, it will allow more gas to compensate.

The car has been getting all scheduled maintenance at the dealership and everything above except for the o2 sensor has been recently serviced, I believe. I will take it back in, but would I be able to save a lot of money if I buy the sensors elsewhere? One other question. I hear that there are two sensors, one on the intake side and one on the exhaust side.

Which one going bad would cause the computer to compensate by adding more fuel to the intake? Or could it be either?

Thanks a bunch for the help