high idle

First: Make sure the PCV system is in good shape, including the oil-separator screen below the PCV valve hole. now to troubleshoot: Then get engine warmed up and disconnect/plug all vacuum ports on intake EXCEPT the fuel pressure reg.

Then stop, disconnect IAC harness, start and check that engine idle is about 500-550 rpm. If above that or still fast idle, you either have a vacuum leak or someone has messed with the stop screw.. but if cold idle is good, I doubt either

I suspect, if idle is good (lower than 650) with IAC plug disc; and the Check engine Light comes on with key on, then goes out, and doesnt show with engine running, you may have a bad Throttle Position Sensor (TPS) - or wiring to it. Bad TPS doesnt set the CEL in EECIV (or most of them, anyway).

If it is still the adjustable version you need borrow a DVM and set it to .90 to .99 volts with the throttle on the stop screw.

Unless it's a weird setup and the PCV is in Valve cover and that hose goes to intake between TB and valves, it's there... back of engine, into cam valley.

The PCV valve:

BYM's procedure doesn't find it, you may have a leak between the upper and lower intake. Problem was mostly in trucks but , not unheard of in cars.

Lugnut

Not likely that the intake problem would/could cause that. You either have a bad vacuum check valve or a vacuum leak in the hvac. This is beyond the manifold. If you have a large leak in the hvac control, it could result in high idle.