I have 2006 scion tc with s/c when I start it up cold it runs fine. after it warms up when I put it in drive it stalls and idles real rough before I can get going. I put it on computer and it reads a po171 code (system to lean bank 1) now is this an o2 problem and if so which one?up by the engine or the downstream sensor. I have a kn intake on it and it was running fine with that on before so I dont think that is the problem. Any help would be greatly appreciated.

 

Bank 1 is usually the second O2 sensor... If your sig has your current mods, the header is causing that code to be thrown since there is not a cat before the second sensor.

Fix: go to Autozone, buy a package of 2 14mm spark plug anti-foulers, drill the flat piece out of one of them (so it looks like a tube), then screw that one into the untouched one. Next, screw the second O2 sensor into the adapter you just made and screw the whole thing into your s-pipe. Clear the code and then start your engine up.

Code should never reappear again.

 

sounds easy enough will try it thanks for the info....