The CO pot was spot on so it would only account for no lambda. at idle it makes no difference as it runs a map, at full throttle it runs a map, its in between (most of the time) it runs rich to save melting a piston, it runs fine this way but yes it drinks fuel and youll lose power slightly due to over fueling but running it very occasional on a Sunday it was fine.
i binned the original manifold about a year but i fitted the engine so i didn't remember seeing the lambda, the intermediate pipe i speak off slides into the jabba system and is connected by a flange that floats on it so it doesn't matter when you fit the welded nut as the pipe will spin round, As long as it doesn't point to the ground it should be ok.
it might also be worth fitting the boost return pipe, the massive air leak past the TB will probably account for someone the "hunting" although the isv is a possibility but be careful finding one as they are pacific to g60. If not might even be worth fitting the new TB.
Other thing you mentioned on another post you changed the Plugs, the plugs in it were only a few mile old and iridium so quite expensive hope you replaced them with proper plugs and not standard cheap ones.
In regard to slight hesitation that was mentioned set the timing up, i never had a timing light so its set static TDC could do with advancing abit should free up some poke, if no light available advance it on the dizzy until you find it pinks then back off a nats will be tiral and error without a timing light though.
