Re: 74mm Throttle Body, surging idle
If I had this surging problem I would reinstall the OEM components and start again.
Before doing that I would study the various seals that are between the engine cover/MAF housing/elbow/throttle body and intake O-ring, also the O-ring on the MAF sensor. A total of five seals if I remember correctly, any one could be faulty.
The ones after the MAF sensor would be most likely to cause trouble I think. The one between the MAF housing and elbow could easily be torn as I recall that was hardest to separate by depressing the clip and tilting the MAF housing.
I assume all the seals are there. I cannot remember if the MAF sensor can be installed upside down, you never know though. LOL