My car is a 1998 nissan altima it has about 170,000 miles on it.

I bought it with 155...

I didn't notice the gas mileage usage until it hit me in the wallet.

The car in the city gets about 14-17 miles to the gallon.

This is HORRIBLE in my opinion as seeing ALOT of SUVs now a days get that much

It's a 2.4 liter, I was wondering what I could do to bump the gas mileage up.

 

When is the last time the car had a tuneup?

 

I have a 99 GXE, so our cars are practically identical. I've boosted my MPG by giving it a tune up, standard stuff i.e. Sparkplugs and wires, fuel filter, oxygen sensor. Instead of replacing the air filter I installed a CAI. Check your tire pressure or buy new tires if they are worn, that makes a big difference in MPG, noise and handling. Also, since you have some high miles, you might treat the engine with a treatment of your choice. I'm sure there is a thread that will argue the differences between Slick 50, Prolong, Duralube, et al.
I used Slick 50. Hope this helps!!

 

There is a website called www.premiuminjectorservices.comThey pretty much clean and rebuild your entire injectors. This dramatically increases gas mileage.