I have an 08 TL-S and have experienced intermittent lean codes (171/174) for several years now. I only get the codes in the colder months when the temp is in the 30's and below. The codes trigger like clockwork, and only in the same situation every time. So I drive to work (roughly 12 miles), turn engine off, car sits for 6 hours, then I drive the car to get lunch, not even 10 min drive, order food and idle in parking lot for roughly 20 min, then drive back to work, turn off engine, so about 30 to 40 min of driving and idling all together while on lunch break. Then car sits for 3 hours till I finish work and start engine up again, leave work and not even 5 minutes down the road the check engine light comes on for the lean codes. The light will stay on the whole ride home and part of the next day, but always turns off until I go through the same work/lunch/home driving sequence again. This is the only time the light comes on and if I do not leave and drive the car to my lunch break, the light does not trigger. I'm kinda baffled as to why it happens only in that situation. Any input as always is greatly appreciated.