My 1988 stock 5.0L manual transmission Mustang has the HEGOs stuck on 0.0- 0.2v at warm idle closed loop with no sensor switching. The sensors are new Bosch and respond to propane enrichment at idle. Above idle around 2200 RPM there is switching. TAB and TAD valves/solenoids check OK. Fuel pressure good and vacuum steady 16 in. at idle. Injector duty cycles are high suggesting ECU command to trim a lean condition, but I can't find the source of any lean conditon (vacuum leaks, PCV, CAP, leaking EGR etc.). ECT and IAT sensors are good. Any suggestions?? KOEO is code 11, system pass. KOER is code for no HEGO switching.