I have a 90 CRX Si with B16 swap. I bought it blown and rebuilt it. It has only one 02 sensor in the mid pipe. The engine cannot find idle, it goes up and down. Normal driving it runs well, should I have two 02's? Or do I have another problem? If I do infact need two sensors, where do I put it? It has a header and aftermarket mid pipe. Do I drill a hole in the header and weld a sensor bung in it? Plus, where do I wire it in? Or is there something else to make an erratic idle? I pulled the IAC valve, cleaned it and ran voltage to it and it clicks so I think it works. Please help!!