I have an 05 LGT sedan 5MT with ~95k, normally tuned to the cobb stage 2 off-the-shelf map.
I recently took it on a road trip from Boston to Cape May, NJ -- that's about 400 miles each way. On the way, the car repeatedly threw the same several codes, as follows (although the car felt perfectly fine to drive):
P1518 - Starter Switch Circuit Low Input
P0852 - Neutral Switch Circuit High
P1153 - Front 02 Sensor Circuit Range/Performance (High) (Bank 1 Sensor 1)
P1152 - Front 02 Sensor Circuit Range/Performance (Low) (Bank 1 Sensor 1)
P0133 - Front 02 Sensor Circuit Slow Response (Bank 1 Sensor 1)
Anyway, since I was away from home, the car felt normal, and I had time pressure and commitments in NJ (I was going down there to shoot a wedding), I decided to go easy on it but still clear the codes with my AP.
When I got back to Boston I noticed that my mpg around town (city driving) was much worse than usual, ~14mpg.
I took the car in and got a new 02 sensor, as I thought that after 95k miles, that was probably the culprit. Since then, the car hasn't thrown any codes at all, and my HIGHWAY gas mileage seems weirdly high, but my CITY gas mileage is still lousy. I flashed down to the stock map (does the ECU need some time to "learn" the new 02 sensor...?). My mileage on the highway since then is still great, and my city mpg is a little better, but I'm still not convinced.