2TR-FE << 2008 pre-runner >> sucky MPG - Bad Sensor?

I could use some input; I have a 2008 Pre-runner access cab with 4 cylinder and manual transmission. Original owner and about 93k miles.

the first 60k miles I averaged 20 mpg city and close to 25 on highway.
I started getting 15 or less in city. I changed air filter, new spark plugs, cleaned the MAF and no improvement. I disconnected the battery to reset the ecu and I got 22 MPG city. over the next few tanks of gas my MPG deteriorated back to bad again.

any ideas on what sensor is malfunctioning? I believe this truck has two (2) O2 sensors

 

You may want to consider getting a cheap obd 2 Bluetooth device. They really help check some of the sensors and in displaying data

 

The Check engine light is not on so it's not putting out a code

 

You can check specs like engine temp and a few others from the sensors. Helps get an better idea than whats just on your dash.

 

thank you!

 

Not placing bets or anything, but it sounds like it is running on a generic map ( limp mode ) which is often due to a flaky O2 Sensor. Get it read and see if there are any Pending Codes... It could be flaky enough to crap up the MPG but not often enough to throw a code.