The IACV on our vehicle has three ports: two for coolant and a third for vacuum. Also, in the troubleshooting section of the manual, it says to put your finger over the lower port in front of the throttle plate to see if the idle drops. Only problem is there is no lower port. It only has an upper port at about 11 o'clock and no lower port at 7 o'clock.

 

Okay, so I replaced the valve with the CORRECT one this time. Now it's right back to where I was when I started it for the first time after replacing the head gasket. Initially high idle (up around 2k!) and then severe surging once I blip the gas. This is driving me insane! I checked all the vacuum lines and they are correctly routed and in good shape. Could it be a vacuum leak in some obscure location or a bad circuit? OR, did I somehow hook things up wrong?

Also, not sure if I mentioned this already or not, but there is no vacuum at the IACV end of the vacuum transfer line from the intake manifold either at idle or with the throttle open. Not sure if that's a determining factor or not.

 

With all you've done, and replaced the IAC valve, you should repeat the base idle setting & force it to re-learn the idle.