Blocking the inlet in no way at all is a diagnostic thing to do.
You have to pressure test to find leaks. That's a fact.
Unblocking an unused vacuum port is weird. Not sure what you are trying to achieve there.
What ecu temp switch in the plenum? Hint ;there isn't one. I suppose you mean the one in the top radiator hose near the plenum.
Stop guessing. Get a multimeter. Check it.