Fuel Mileage drop in 03 Tacoma, Help!

[Hoosier 45]

Hi all,
At about 70K I had a check engine light come on. At the time I was getting above 19 mpg back and forth to work (if I was really easy on it) and up to 25 on longer road trips at 55 mph. I drive like grand ma but it saves fuel. Anyway, Two dofferent parts stores computers said it was a front 02 sensor. I changed the O2 sensor the light stayed off after reset but my fuel mileage is down to 16 to work and 21 on the road. That is a drop of about 20%.
I checked the engine coolant temp sensor, it was reading to spec. I have driven at hiway speed for 15 miles then felt all 4 wheels brake drum/rotors, cool to touch. Iam stuck, any thought?
Thanks

 

[SGV]

I believe there is a second O2 sensor. That could be the problem.

http://www.lieblweb.com/tacoma/Mechanical/O2Replacement/02Replacement.html

 

[Hoosier 45]

Yes there is but both diagnostics said the front one and when I replaced it the check engine light stayed off. If the back one is bad would the light stay off?

 

[VtFly]

How many mile driven since the O2 sensor was replaced. Have you given the ECU time to reset?

 

[Hoosier 45]

I would guess 5 -7 hundred.

 

[mtnbike28]

In the NE?

with a name like Hoosier are you in the NE? I always drop 20% mpg in teh winter.. something about the fuel blend...

Just a thought

 

[Hoosier 45]

Indiana, would a winter blend cause that big of a drop?

 

[mtnbike28]

mine does...

I record every tank... to make myself feel better, I look back at the summer mpg... I am down to 16mpg right now, same as last winter... in the summer I am about 19mpg.

 

[WhereTheHellIsJames?]

Are you buying your fuel at the same location? If so, have they recently changed to a higher ethanol content in their fuels?

 

[Hoosier 45]

Good thoughts, I have bought fuel here and there, I guess I sometime try to make things too difficult. It is just with these modern engines i keep thinking there is a sensor sending faulty info to the computer.

 

[Switch]

Low tire pressure will kill mileage. I'm sure you checked that but sometimes the easy stuff gets overlooked.

 

[Applejack]

Remember, since cool air is more dense, your computer will automatically adjust for more fuel to mix with it. It could be that since your O2 sensor was bad, your truck was running lean and thus using less fuel. I always get crappier mileage in the winter, and it isn't all from winterized gas blends, though they def. contribute.

 

[clintr]

During the winter months the fuel companies decrease the oxygen content because of the colder weather. My 4runner also dropped 3 mpg since November and I too was asking myself, " what the hell is wrong". After researching, I finally found out why. But I did use concentrated fuel injection clearner and now put 100% gas instead of ethanol.

 

[teotwaki]

While you are at it go ahead and clean the Mass Air Flow sensor too. :sombrero::

 

[Hoosier 45]

How do you clean it?