High ltft, occasional check engine light

Hi
got a 2008 Toyota Avalon a couple weeks ago with 145,000 miles. Don’t know any history, except for annoil
cjange was done 2/23 at 144k miles so likely the car sat

it drives fine, idles between 6-700. No stuttering, no stalling. 

I do have a fuel/exhaust smell. 

after first tank fill up I got code p2195 for b1s1 stuck lean. After clearing and more driving, I got code p0135 for b1s2 high voltage. That code was pending and has cleared itself. My issue is still bad mpg, and a strong exhaust smell. No obvious exhaust leak as it’s quiet and sounds normal.  I smoke tested the intake lines after maf, no leak. 

my bank 1 Ltft at idle is 12.5. As I drive it goes up to 20+. If I step down hard on the pedal, it drops to 4. Currently no cel, all monitors are ready, except for oxygen sensor monitor. In mode 6, it has no values for bank 1 sensor 2. 

bank 2 ltft is normal range. 

am I right to suspect a bad downstream o2,

any likelihood of a bad intake plenum?

im on second tank of gas since purchase. 

Based on the fact that it is a single bank issue, a fixed lean B1S1 and a rich B1S2, and the smell of fuel.

You should suspect the B1S1 is either biased lean, or there is an exhaust leak upstream up it.

Put a shop vac in blow mode in the tailpipe and use soapy water spray to check for leaks upstream of the sensor, (might as well check everywhere while your at it)

If you have leaks ahead of the sensor you fix that first, because this is creating a FALSE lean condition so the PCM over fuels and your B1S2 goes RICH and you smell fuel.

If there are no exhaust leaks, and it is easy to do, swap both Pre-Cat O2's and see if the problem moves to bank 2.  If it does get a new sensor.  
If it doesn't other checks will be required.

Thank you for your insight. I was able to smoke test the exhaust system. Inserted smoke machine end in one muffler, and blocked off the other. I found a leak in the front pipe where the hanger bracket is welded to the pipe. Based on your input, I think that leak is what’s causing b1s2 to demand extra fuel.

I also found a second leak further back where the pipes split to go to each muffler, also where the hanger bracket is welded on. I plan on taking it to a muffler shop to have them seal these holes up and I’ll check on trims again.