replace your thermostat asap. your engine is not running at optimal temp., so yes, that will affect gas mileage. it doesn't hurt to replace the cap and rotor either. if they're sufficiently worn, your spark will likely not be as strong, leading to less than ideal combustion.

bad o2 sensor can affect things as well. see about getting that fixed.

 

How is the ECU reset?

 

For a CRX or 3rd Gen Integra.

For 98+ Integras

-Turn the ignition switch off. Remove the BACK UP (RADIO)(7.5A) fuse from the under-hood fuse/relay box for 10 seconds. Be sure to have the code for the radio if you still have the factory unit.

Team Integra ECU reset article

 

your cat can be bad

 

also maybe a better airfilter will help

 

If my cat were bad, wouldn't I be able to tell? I thought it was supposed to smell like sulfur when your cat goes out or something...Also, my Intake Air Temp Sensor has been broken off ever since I bought the car. Could this be a big contributing factor too?

 

well it could be clogged

 

There are check engine light codes for both the cataytic converter and intake air temperature sensor. If there was something wrong with either of them I would hope that the ECU would figure that out and throw a CEL.

 

i dont think it would if it was clogged, get a pen and tap the cat and see what you hear

 

Right now, I'm just throwing codes for my O2 sensor and IAT sensor...