I am having trouble with unstable rpm, especially at idle. I can feel it on closed throttle coasting very slightly, more noticeable at idle in gear and more again in park. I have worked a lot on the ve tables and at normal cruise my blm's sit pretty close to 128 and don't move much. I have just installed a wide band o2. A/F at cruise shows roughly 14.1 to 14.9. Idle shows 13.5 to 15.2. O2 voltage is roughly .085 to .850 at idle and .165 to .875 at cruise. I thought maybe the o2 and headers was a problem so I installed a heated narrow band. No change. The idle fluctuation caused the IAC to dance around so I got the IAC to zero and disconnected it. Helped at bit but not acceptable. I have read on forums that P4 pcms have overly active o2 handling. I have set and unset closed loop idle. No change. In the data stream closed loop always shows and it seems as though it is being controlled by the o2 even when I think it should be open loop at idle. Today I disconnected the NB and it drove great. Cruise the WB showed 14.7-14.9, foot off coasting 15.2-15.3, idle 13.7-13.9, no light throttle surge and idle rpm stable. I said it was going to be long. It is perfectly driveable right now in open loop but that won't last for weather changes. I don't speak GM so don't know what a lot of the o2 parameters mean and things are pretty sparse regarding documentation. So anyone have any ideas? My next move is to install one of my mega squirts and let it look after fuel and ignition, trans and IAC on 6395. Is there any way to slow the NB response down and being as my wide band has a second channel is there any way to control with that?
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