I have a 91 EF with a D16Z6 and OBD1 swap, and so far all the issues I've had getting it to run right have been resolved, except for an odd warm up problem. With the engine cold and the ECU just reset, it'll throw a code 1 (O2 sensor), and have a rough idle. It'll start to idle around 2k, then work its way back down to 1k within a few seconds. There's an Autometer Lambda gauge hooked up, and it starts out in the rich/stoic area, and then gradually tapers down into the lean area as the engine settles down to about a 1k idle. If I hit the gas, it'll hesitate, but will rev up. After the engine is warmed up, I shut off the engine and take the keys out, then put them back in to see that the code 1 has disappeared. If I start it up now, it'll idle and run fine, but the lambda gauge is still reading lean. Any ideas on whats creating the code 1? Is it normal for the gauge to read lean on idle with no load? Thanks in advance.