Re: 74mm Throttle Body, surging idle
I would check that all the fittings are on properly, like the two hoses from the valve covers and how they are on the 'Y' fitting on top of the TB, and that the 'Y' is in the TB correctly. The O-ring between the TB and inlet should be new as the old one gets deformed and will fail to seal once it is disturbed.
Failure to seat the engine cover on the MAF housing can cause trouble if it is not on tight. Mine was loose when I got the car but caused no problem.
Also check the two electrical connections on the MAF and TB.
Lastly the new TB could be bad, so you could go back to the OEM and see if that cures the problem.
Very frustrating though.