I recently replaced the bank 1 O2 sensor on my 03 HCH because I had taken it to the dealer and they had wanted to order an O2 sensor for $412 w/o tax or labor. So I order it online and changed it out w/o a problem. I erased the existing error code then did a diagnostic check and it passed just fine. Then I went to start the engine and immediately after it turned over it redlined. So I put the old O2 sensor back in and it did the same thing. It seemed like there was something wrong w/ the throttle position body/sensor or accelerator cable. So I got to the the throttle position body and w/ the help of my father pressing on the gas pedal saw that there was nothing wrong with either the throttle body/accelerator cable because it was moving+returning fine and nothing was binding. So at this point i'm baffled and assume its the throttle position sensor. Any help/advice on how to begin to troubleshoot this problem would be greatly appreciated. Thanks - Ben

 

I don't think the engine can redline without the throttle plate being open. I think the throttle plate is sticking open when you start the engine. Make sure the plate is fully closed and then start the engine without pushing the throttle pedal. Does the engine still redline?