First off, I have a '99 LX M/T. I used to get 40 MPG highway, but now its running about 32. I was wondering what could cause this. Do I need a new fuel filter? Clean the fuel injectors? The sparkplugs in it are new, same with the air filter. And if I do need a new fuel filter, is there a service manual online that can show me how to do it?

 

Do you race around a lot?? What mods have you done?

 

Don't race, no mods.

 

Is your CEL on?

Changing your fuel filter can help or restore your MPG. Many factors could cause the car to have poor mpg like alignment, poor spark and etc. Give it a basic tune up.

 

Low tire pressure could also contribute to low MPG. Make sure the tires are inflated to ~35 psi.

 

I was about to say that...awesome. You can also change the cap and rotor to get better spark and that will help also

 

Have you run Seafoam yet? I would give that a try and see if its still giving you bad MPG.

 

Seafoam? I guess I will google it.

 

No the check engine light is not on. I'll check the tires, but they seemed fine since i just recently added air to them.

 

Why dont you tell us what you have done to help with MPG. We will tell you what may need to be done after you list them all.