[TonyS9]

Seems you at having a good go at diagnostics but some of your basics are a bit off.

A rich mixture cannot cause a high idle in a spark engine. If you add air and the idle drops it means the mixture is correct or weak. Adding air to a rich mixture is what happens when you open the throttle.

If the idle is high with the IAC pipe clamped,, its because you have too much air getting in. A smoke test is the right thing to do but it' doesn't seem to be showing up the problem. Try again look harder.

The clamp test does indicate its a leak and not the ECU doing it deliberately, it can do this if it thinks the auto drive or AC has been engaged.