Ok, I thought I'd make a huge list of things you can do to improve your gas mileage since everyone is always asking about this. So go ahead and post your suggestions and I'll just keep editing the first post to include them all. Thanks!

External Factors
1. It goes without saying, don't race your car around. Drive conservatively.
2. Keep it under 70mph. (wind resistance + high rpm in cruising are bad)
3. Drive with your windows closed. (wind resistance)
4. Stop using the A/C so much... or at least get it checked to make sure it's still efficient.

Suspension

1. Get an alignment! Anything that prevents your car from rolling straight will rob power and create resistance (from your tires wearing out prematurely).

2. Fix your bushings! This is my own belief and here's why... I had a bunch of crap in my back seat and trunk that was weighing my car down. Now you might think it was just the weight, but I think it's also why my rear tires have worn out prematurely. During this time I also had severely bad gas mileage (25-30 mpg). Somehow, my tires had negative camber with all the weight because all the wear was on the side walls on the outside. I since removed the boxes and crap and magically my gas mileage is improving (without fixing the bushings... yet).

3. Check your tire pressure to make sure it's right.

4. Make sure brakes are in good order and not sticking. This goes for the emergency brake too. Lift your car up and try to spin the wheels. If they have any resistance (they slow down too fast) then something is wrong.

Engine
1. Get a new o2 sensor. If they go bad, you will definitely have bad gas mileage. But if they're giving low voltages because its dirty, your ecu will think you are going lean and will dump more fuel to compensate. Check your muffler tip to see... it will be BLACK, not dark gray.

2. Change your PCV valve.

3. Check and correct your timing at the distributor with a timing light.

4. Get rid of that eBay chip. It's crap... go back to stock or get it professionally tuned.

5. Change/clean your air filter. Get a K&N to replace a stock air filter.

6. If you're turbo, get rid of the FMU and the piggyback. Get a professional tune using Crome/Uberdata/Hondata/Turboedit/Neptune. Or do it yourself with a wideband o2 sensor.

7. A clogged fuel filter will ruin your mileage.

8. Check valve lash when the manual says to.

9. Check/change spark plugs. All you need are NGK copper V-power plugs. Nothing fancy.

10. Don't wait forever to change your oil. Also watch oil level.


(got this off another forum, thought I'd share since summer is coming)

 

buy a motorcycle.

 

Swap in a diesel motor.

 

Walk.

 

Retard timing if it was advanced before.

OR ride a bike.

 

Avoid using the brakes. Seriously. It takes gas to accelerate your car and once moving, you want to sustain your momentum to get you where you are going, instead of stopping and accelerating all over again. So when you're coming up to a stop light, let off the gas, and begin braking while you're still pretty far away. Try to time it so that you can maintain as much momentum as possible. Remember that if there are cars in front of you, it will take time for them to get going once the light turns green. However, if you are coasting up to a red light and the person behind you wants to make the green left turn arrow, don't be a dick.
When stuck in traffic, leave a buffer zone between you and the car in front of you. Every time you get too close and have to brake, you're scrubbing off valuable momentum. If traffic is doing the stop-and-go thing, then try and maintain the average pace instead of using the accelerator and brake alternately.

 

im not tailgating, im drafting

 

if you had severe negative camber, the wear would be on the inside of the tire.

 

the average car uses 20% more fuel at 70 mph then at 55mph, but its going 27% faster, improvement of 7%. i got from south brunswick NJ, to West Point VA on one 12gallon tank of gas, with JDM gears (much smaller 55 is 3k rpm in 5th), and an OBD1 JDM GSR, at an average speed of 80mph, a couple of 8000+rpm races from a stop to freeway speed at a toll booth, and a bunch of stop and go by DC and baltimore. (average 37mpg, 330+miles)

 

Speak for yoursefl at 70mph my tach is at 2k