Gas mileage - '96 2.4L

Hello all,

I recently purchased a '96 Grand Am SE with the 2.4L engine. My initial MPG was averaging about 20-21 mpg. The spark plugs were old and worn down quite a bit (one of them was worn down so much it started misfiring)...so I ended up replacing all 4 plugs and boots last week. I was hoping this would improve my gas mileage at least a little bit, but initial results indicate that the gas mileage has not changed. First tank after replacing the plugs came out to about 20.4 mpg.

Is this MPG normal for this car? Should I be expecting it to be better? Any tips on improving it? The air filter isn't that dirty, but I'll probably replace it anyway when I next get paid. The check engine light came on last week - the code is for the heated oxygen sensor behind the cat.....would this be affecting the gas mileage any?

Thanks in advance for any help/tips you can provide!

Yup o2 sensor will cause poor mileage. Also, automatic or manual? City driving or on the highway? My 95 gt 2.3 gets around 36 on the highway with the cruise set for 70. In town I get around 22-23, less if its snowing.

Automatic.

Mixed driving. 3 days a week I drive about 60 miles each way back and forth to work (55 of which are highway miles)...the rest of the time is city driving, shorter trips. On average, I'd say each tank of gas probably goes 2/3 to highway driving and 1/3 to city driving.

the car is rated at about 20mpg city and 24mpg highway (i have a 1997 and thats what the orignal window sticker says)

My 96 2.4 (manual) has been retired recently from my ownership at just over 245,000 miles. Has a little trouble last winter where things had to be replaced and I ended up with one new coil pack, both O2 sensors, and catalytic converter. The one time after that I caluated MPG (only one tankful) it ended up at 33MPG. Most of my driving is either highway or what I'd call rural/surburban (not many lights or stop signs and speed limits of 35-45)