Mpg random change

Hey all
I've had my 19 cm with aftermarket air filter for 2 years now. Had no problems until the last month or so and only getting 10 to 11 mpg.
I have no codes, air filters are clean any idea why I'm getting such low mpg?

 

You might want to do an oil analysis to check for silica.

 

Dry or oiled air filter?

 

Driveline lube lately? Brakes could be dragging also, that was an issue on my taco.

 

Dry air filter no brake or driveline lube lately
I went from 508 to 401 on a 38g tank of gas

 

Is that actual calculations or are you relying on the dashboard readings?

 

My last trip Sunday was 397

 

Is it a Flex Fuel tundra? If so get an OBD2 reader and pull your Fuel Alcohol %. Should be 0. When mine spiked I dropped in MPG. There are a few ways to reset it, there's a thread on it.

 

I would hand calculate the miles on a tank and divide by how many gallons you put in. You’re not using 38gal of fuel on a tank.

 

Assuming you are not flex fuel and the mpg is calculated by you, the first place I would be looking is the two upstream O2 sensors. They can fail quickly and the mpg can drop like a stone when they do.

 

Neighbors stealing your gas??? Jk would try a bottle of sea foam in the gas, clean your MAF sensor with MAF spray, clean the throttle body plate, check for vacuum leaks (computer adds fuel to compensate), replace your pcv valve, check wiring for the purge valve, try a tank of ethanol free to see if the issue is winter blend/local ethanol change.

 

Winter Blend of gas can reduce MPG.
Since mine is not in the Garage, I let mine warm up a little longer in the winter which also reduces the MPG since I am using gas at idle.

 

^^ what Bergy said. Just from idling a few minutes in the morning and running winter gas. Could be small change in tire pressure also due to colder weather. I lose about 1.5-2 mpg during the winter months in Louisiana, I'm sure its a lot worse further up north.

 

I could be wrong but I think my scan tool said I was using .5 gallons fuel per hour while idling.