Hi Ricky, yes a wideband O2 sensor in one collector, with closed loop feedback, although for setting up, I change to open loop so that it's not far away from where it should be, then change back to closed loop.
I am convinced that the black smoke was fuel pooled in the inlets and fouled plugs from the previous day, the entrance to the garage is an uphill slope, so having messed about at idle all day, then stalled a couple of times getting back into the garage, the plugs were fouled and there was a lot of fuel in the inlets. So in the morning on cold start, with cranking enrichment, it made clouds of black smoke, then suddenly cleared and idled sweetly again.
I have monitored the sensor both with the Emerald Data Logger and a separate lambda gauge and O2 sensor readings are as expected, ecu maintains target from idle.
yes, I drive along and all is sweet, but to be exact, if I throttle off and dip the clutch at 1500rpm+, the engine will undershoot idle and sometimes stall. If I throttle off and dip the clutch at 1000rpm or less, it doesn't undershoot and idles ok.
Yes, I like that idea, switching to open loop would have told me if the hunting was driven by the ecu or not, I will try that if it hunts again.
The hunting and the stalling seem to be separate issues and once I cleaned the plugs, it didnt hunt again, but it still undershot idle target when I dip the clutch at 1500rpm.
On thing that seemed to work inconsistently was the idle control by ignition advance, I had set idle to 900rpm, programmed to the ecu but it still idled at 500rpm, then another time it went up to 900rpm as expected, so I need to look more carefully at that, and get a new set of plugs, or two or three sets as my friend suggested.
I don't think there is a vacuum leak, but ultimately might strip to replace gaskets. I nearly did a compression check but was running out of time, I might do that later, but engine pulls well so I doubt it's that. Looking like fouled plugs, not so good ecu settings resulting in poor idle control, but can't be sure just yet.
On a lighter note, the guy who came to help me has a '69 Corvette and does his own road tuning which is why I contacted him for this, he is installing an LS3 with forged components, looking to make 1000hp on twin turbos.
Dave