I have an 04 and I recently bought a new engine harness for the same year 03-05 non rev up. I had 2 codes p0031 and 37 since I received the car and changed the ecu, o2 sensors, installed bungs on top of the bungs from the z1 hi flo cats. I then recently got a code for p1148. I figured my harness was shorted somewhere or open so instead of figuring out where it was I decided to just change the entire harness. Disconnected the battery for some time and got to work. I figured a used and tested to work harness would be fine and I turn the car on and it’s much lower in exhaust tone and it seems to be running rich as it popped the moment I started it and seems to when I rev it. I know this might be broad but any help at all would be very appreciated as I don’t know what to do anymore. I will be happy to answer any questions.

 

Probably have two of the coil plug swapped. Very easy to do. Check the two rear ones on the driver's side.