So I bought the car a while back and it's been throwing a code for O2 sensor which it doesn't even have one. This is a tune problem... so you need to really identify your ECU... and if it is tunable or a stock ECU. The car runs fine (appears to be fine) other than the poor gas mileage due to it idling at 1200 rpm's. The car is not getting poor fuel economy because the idle is high... it is a combination of an improper tune and the lack of an O2 sensor. So my question is if I buy a new O2 sensor will this correct the high idle? No, not likely. I've messed with the idle screw and it does nothing. It has paint on it for a reason... it is not meant to be adjusted. If you can put it back as it was, you will be better prepared to actually find the real problem. Also I have a aftermarket header do I order a O2 sensor for a 98 civic ex or a 98 prelude and will it be long enough to reach the hole on the header or do I have to extend the wires. It will depend on where the O2 sensor bung in the header is and the distance between there and the four-wire O2 sensor plug on the engine harness. It is likely that an extension harness will be necessary. Any help is appreciated

it's a chipped P28 with the OBD2-OBD1 conversation harness but I will take a picture tomorrow.