O2 #1 and #2 signals look good at the ECU terminals. (I have ELM323 OBD reader but I'm not convinced that it is giving me the correct information. it doesn't like O2 #2 (0.000v all the time). But O2 #2 just replaced with new Bosch OEM and the voltage at the ECU is 0.2 - 0.8v.

Car idles (750RPM on the nose), revs, and powers very nicely while the fuel system is running in open loop mode. When it enters closed loop mode there is hesitation and stalling when slowing to a stop and when coming off idle. No MIL or codes after driving for about 20 minutes.

I also feel a strange periodic loss of power (with accompanying fluttering noise that seems to be coming from the exhaust side) when powering up an incline. smooth then a second or so of fluttering then a pause of a few seconds then repeats for a couple of times.

The vacuum line to the purge valve has just been connected today. Could running previously w/o vacuum to the evap canister have caused a buildup of vapor pressure? Any chance that this strange fluttering is occuring when the purge valve is opened and the mixture is going way rich?

 

I'm beginning to suspect a bad ECU - still having problems when the fuel system goes into closed loop mode, reporting that Bank 1 #2 HO2S is bad. But I've measured voltages at the ECU connector for both sensors and the signals look like they are the correct levels. #1 sensor varies quiet nicely 0.2 - 0.8, #2 sensor seems trained on .45V with very little change.

Does anyone know what the ECU criteria for good HO2S sensor on #2? (post cat convertor). That sensor is new Bosch OEM and I've checked every inch of wiring from the connector back to the ECU.