I recently bought the 97prizm with the pos 3 speed automatic, just because it was a good price and i can share the car with my mom, so its 2x the savings on inusrance and tabs. got it for 1250, with new tires, ran perfect, no rust or sun damage.
i just got thru a tank, its about 70% city, and about 30% highway going at 60 mph. i really didnt expect it to be at 23mpg, even my friends 06 CRV 4x4 gets that kind of mileage, while being a crapload bigger, and heavier.
and no, i dont have a lead foot. I was getting 45 mpg all the time with a 94 civic dx stick, with the short geared ex tranny. the prizm has a extremely tall 1st gear, and on 3rd gear, 60 mph is at 3000 rpm, and 70 mph is at 3500 on the scanguage.
so far i have 44 psi tires, intake, changed out all the fluids since i bought it, and putting the car on N when at a light. is there any other advice out there that can help me?
I have driven a 90 civic auto before, i was getting 33 mpg with that, i was really expecting to get at least 25 mpg at worst case.
It is 11 years old and if you don't know the prior owner and or have maintenance records you would have no way to know how it was treated/maintained.
A really complete tune up would then seem to be in order including plugs, wires , dist cap etc, etc, don't forget the pcv valve and air and gas filters. Verify 02 sensor operation as was mentioned. Then change all fluids. That should at least do two things. Give you a baseline of when everything was done, and also maximize your fuel economy. It wouldn't cost much, and is real easy to do on that car.
You said it was a 3 speed auto so it does not really have an overdrive. Maybe some more experimenting with speed/rpm and you will find it's "sweet spot".
Also if you get "winter blend gas" where you are, that could be contributing to a lesser gas mileage.
I wouldn't worry too much about the O2 sensor. OBD2 does a good job of telling when that sensor is dead. It does get slower, but you won't see any real increase unless the sensor is so bad that it trips the MIL.
dragging caliper, bad bearing, bad alignment, underinflated tires, bad grounds, sensor problems (don't always trip a code IE coolant temp sensor reading low but still reading) (can be from bad grounds)
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"