14 MPG!! :( car runs fine, PLEASE HELP - Scionlife.com


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Old 09-12-2017, 07:49 PM   #1
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Exclamation 14 MPG!! :( car runs fine, PLEASE HELP

Hello all!

I’m in college and I recently broke the bank to buy an 05 Scion tC manual to be my commuter car. 165k. Almost immediately I noticed how bad the gas mileage was. On the hour drive home I could watch the needle go down driving on the highway and almost ran out of gas on the way.

Recently I hooked up my OBDII sensor to the PCM to find out how bad it actually was, and on my 18 minute drive from my house to school, (40 mph average) I got 14 MPG!!!!! At a half of a tank I’m at 84 miles on the trip. I’m a fairly conservative driver, usually shifting around 3.5-4k in rush hour. (I have stock rims, and tires are the correct size and pressure)

With that same OBDII sensor, I decided to check the code history, and it popped up with B2799 and P0138. P0138 is an oxygen sensor, but I’m not sure if it’s the one that controls A/F ratio, if it is, could it be a bad sensor throwing of my A/F? I have no CELs right now, does that rule that possibility out for sure? B2799 is a faulty key code so I think that’s a non-factor.

I’ve looked into it and I plan to change my air filter, clean the MAF sensor, get new plugs, new PCV valve, change my oil. I’ve looked at my air filter and it doesn’t look that dirty, not nearly enough to cut my mileage in HALF… I don’t smell any gas fumes anywhere around the car when it’s off or running, so I don’t think it’s a leaking tank or fuel injectors. The weird thing is the car is running fine. Idle is smooth. It does take around 6-8 spins of my starter before the car fires up but I’ve been told that’s just a Toyota thing so idk.

Has anyone had a similar problem? Any other suggestions? Please help. I don’t want to have to rack up a mechanic bill when I can barely pay for school.

Last edited by MR_LUV; 09-13-2017 at 10:16 AM. Reason: typo
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Old 09-12-2017, 08:26 PM   #2
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Maybe use the OBDII to check your long term and short term fuel trims. Jack your car up and spin the wheels to make sure a caliper isn't hanging.
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