ryan s
they dont think it
ironically, i just replaced the evap bypass sensor on my dad's TL last night 
i noticed sitting in the car that there was a thumping noise at idle, so i got out and its coming from the rear evaporative section (immediately in front of the gas tank).
it sounds like someone is tapping their thumb on the large plastic evap tank, probably 3 times/second.
i've had the P1456 come and go for the past few years in the summer, but it hasn't shown up in the past couple months. no CEL now, but i havent driven it over 40MPH since i discovered it.
otherwise, the car is having an idling issue when switching gears...only into first, the other gears are fine. mileage is good, runs fine except at idle speed.
what could it be? i have a TL printout but its not very good quality, but at least i can see most item locations to get started.

i noticed sitting in the car that there was a thumping noise at idle, so i got out and its coming from the rear evaporative section (immediately in front of the gas tank).
it sounds like someone is tapping their thumb on the large plastic evap tank, probably 3 times/second.
i've had the P1456 come and go for the past few years in the summer, but it hasn't shown up in the past couple months. no CEL now, but i havent driven it over 40MPH since i discovered it.
otherwise, the car is having an idling issue when switching gears...only into first, the other gears are fine. mileage is good, runs fine except at idle speed.
what could it be? i have a TL printout but its not very good quality, but at least i can see most item locations to get started.