I just had a B16 (first gen from an SIR) swapped into my 91 Rex (which was a DX previously). Although not strictly part of the swap, at the time I upgraded I/H/E for aftermarket. The header is a DC Sports 4-1 version (more on this later). Everything was running great for the first couple of weeks. Had it tuned and she purred like a kitten... That was then, this is now. When the engine is cold everything is perfect (or as perfect as can be expected) engine is a little rough, but not anything out of the ordinary. The problem only occurs when the engine is all warmed up - and even then only part of the time. When I give it decent throttle - not full, but about half way on the accelerator in any gear (but much more noticible in higher gears since they're longer) the engine will shudder as if it's running WAY too lean... and the power will be less than half what it should be. If I stay on it - the problem 'rights' itself within 5-8 seconds and then the engine sound returns to normal and the pull is good until the next shift... then back to normal. If I just barely give it any gas and wait until I get a little higher in the gear (~4000RPM or so) and then open it up the problem very rarely occurs. OK so that's it for the problem... now what to do about it. At the beginning of my post I mentioned that I put the DC Sports header on, well it only has 1 O2 bung instead of the 2 that came stock on the OBD0 B16's... I had this done at the time of the swap, so I haven't been able to determine where they spliced the wires yet (or if they did even). I'm thinking this is a problem with using a one-wire O2 sensor farther down the exhaust line (since not as hot as in the runners and it's not a heated O2 sensor like OBD1 uses). Is it possible that this is just a bad O2 sensor (has anyone run a spliced 1 wire O2 on B16/PW0 setup with no problems) or should I go ahead and custom set up a 4-wire O2 or am I completely off base.