low gas mileage?

[BailOut]

Edit: I see now that much of what I said below is repeat information, except the DFCO stuff. As such I'll make a separate DFCO usage thread.

We should probably have a forum dedicated to fuel economy but I'll throw a few things out here. Some of this has already been said but it's my checklist:

1) Check your tire pressure. It should be between 32 and 35 PSI on all 4 tires.

2) Check your air filter. If it's not white to off-white in color have it replaced. Also consider going to an aftermarket filter with better breathability (i.e. K&N).

3) If you buy cheap, off-brand gas, stop it. Cheaper fuels are priced so because they use additives and detergents, etc. with much lower caloric content than you find in the primary fuel brands and end up costing you more money than primary brands due to lost mileage. The folks over at PriusChat did some extensive testing and found that Shell provides the best bang for the buck, with Chevron in a close second, and others like Texaco, Mobil1, Diamond Shamrock, etc. close behind that. As of the time I wrote this post Shell gas is about USD $0.15 cheaper per gallon than Chevron so it's definitely the best choice.

4) Make sure your hand brake is fully disengaging by engaging and then disengaging it on a very slight grade (as in a road that just barely goes downhill) and seeing if you start to roll downhill or not.

5) Don't go too lightly on the throttle while accelerating (but do shift early so that you don't get into the higher RPM's, if you can help it), but go as light as you can at the highest gear you can (without bogging the engine) once you're at speed. This is because acceleration requires much more energy and in an ICE our energy comes from fuel, and more fuel requires more air. If your throttle body intake valve is mostly closed because you're not on the throttle then your engine has to work that much harder to create more of a vacuum to suck air past the mostly-closed intake valve.

6) Learn to use DFCO to your advantage. DFCO stand for "Deceleration Fuel Cut Off", and it is manifested by your ECU stopping all fuel flow to the injectors and all spark signals to the coil packs when you are in gear (with the MT just be in gear with the clutch disengaged, with an AT pick a gear other then OD, i.e. 3) and decelerating (engine braking) with the throttle at 0% (take your foot entirely off the accelerator). This is not a feature unique to the Yaris (you can test for DFCO in any vehicle made since the early 90's by going down a grade while engine braking and then turning off the ignition (Be VERY CAREFUL when you do this as you may lose PB/PS... don't cause an accident!)). If you feel no difference in your deceleration g-force when the ignition is on or off then your engine is using DFCO. DFCO can be used on anything from downhill grades to highway offramps to approaching a stop light or stop sign. Use DFCO instead of engaging the clutch and friction braking whenever possible, all the way down to just a few MPH. Remember: DFCO uses no fuel while idling does, so never idle if you're moving forward.

7) Anticipate stops and try to work around them as much as you can. Stop signs are the worst because they are guaranteed forced stops (unless you're a Californian, in which case it's just a modified Yield sign, and this is why your insurance costs so much) but traffic lights and heavy traffic can often be worked around. Never jeopardize your safety or the safety of others for the sake of MPG, but using DFCO while you approach a red light gives you the chance to still be doing 10 or 20 MPH when the light changes and traffic begins to move. Keeping a few car lengths open ahead of you in heavy stop-and-go traffic lets you keep forward momentum, even if it's just around 15-20 MPH, and you can use high-gear DFCO to slowly decelerate when needed.

8) Don't speed. Every 5 MPH over 45 takes an average of 5% more fuel to achieve. Actually going 55 MPH instead of 65 in a 55 zone can save you as much as a half gallon per tank. Ignore tailgaters as they'll stick on your ass at 50 as much as they will at 70, but be sure to give them passing room when it's appropriate.

9) Consider some of the other advanced fluids and chemicals that are available to you. Mobil1 synthetic oils, Lucas Oil Stabilizer, Lucas Fuel Treatment, etc. For example, Lucas Fuel Treatment (which is a chemical optimizer and fuel system cleaner/lubricant. not a cheesy octane booster) costs $3 for a 5.25oz. bottle at Kragen. You only need half that bottle in a full tank of fuel (the whole 5.25oz. treats up to 25 gallons) and for my friends and I it tends to produce an extra 2-5 MPG, even on winter gas. With gas prices around $3/gallon you're guaranteed to break even (and have the caloric equivalent of an extra half gallon of fuel in your tank), but you also have the potential to get an extra 20-30 miles per tank beyond the break-even point (and some folks choose to use it only every 3rd or 4th tank).

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I just bought my 2007 Yaris Liftback (with the 5-speed MT) a few weeks ago on 02/21/2007 and it will not even hit 1,000 miles until next weekend. My daily commute is 27.2 miles one way over a mountain which I climb from 4,500ft to 8,900ft, then descend to 6,300ft, and I'm basically on that climb within 1.3mi of leaving my home. We're still on "winter gas" (10% oxygenated ethanol) through the end of March and this hurts MPG by a bit as you're basically losing ~10% of the fuel's caloric content, and the only modification I've made to my Yaris so far was a K&N air filter on the first tank and the Lucas Fuel Treatment on the second tank. I also gained a better feel for using the DFCO throughout that time and have gotten to the point that I can get down either side of the mountain without ever touching the throttle and using the friction brakes just 3 or 4 times.

My MPG on the first tank was 38.97 and on the 2nd tank was 43.67.