Lambda isn’t used until it’s warmed up and goes closed loop. Again, it’s not used at Wot either. With your big maf, have you checked your Iat are sensible ? Both in the maf and the inlet elbow.

But air leaks are the most common cause of poor idle. The revs going up and down is called hunting as the ecu tries to get the idle as low as it can.

Classic poor idle causes.

Gummed up idle control valve, they seize up. Not that likely but I’ve had one.
The crank case vapour recovery hoses split, Very common.
The check valve in the recovery hose stick.
Pcv valves stick.
Brake servo diaphragm leak.
There is a blanking plug on the ports on the back of the manifold. These perish.
Reference hose for the Fpr.
Reference hose for the map.

You Can blank these of one at time to see if it changes anything at idle.

Dirty injectors dribbling.

Have you had your fuel pressure checked. Pump or Fpr could be dropping pressure.

Re torquing the mani, being plastic it only needs nipping up.

And then there is the Mapping. What spec are you running to need the big maf ?

Shame your not local mate.