I can get to my AAV (item 39 in the CIS diagram in my signature) without removing anything. There are two 10mm nuts that hold it to it's bracket. Y0u can't see it, but you can feel it. Be careful you don't drop the nuts. It won't be terrible, but I hate loosing my nuts in my engine compartment
You should be able to see it on the right side of the CIS just above and behind cylinder #6.
(I have a '78 SC engine in my "mid-year" too.)
The thermotime switch (17A in the CIS diagram in my signature) looks like a connector with a round portion about the size of a US quarter. It has two wires (in a connector) connected to it with vacuum hose (8 or 10 mm hoses) going to and from it. It should be bolted to a bracket on the left side on the number 3 runner.
I pretty sure my thermo valve is crapped out. My CIS is alittle bastardized, so I have compensated for it. I haven't noticed that it makes a huge affect on the start up or running of the engine.
The thermo time switch is mounted on the left chain housing. You'll see it sticking out of the chain housing with two wires on spade connectors on it. I don't think it is part of your problem since you have good warm start. But then again if it is faulty, it will prevent your coldstart valve from spraying on cold start which is not need during warm start (see it in the wiring diagram in my signature). You can test it for resistance. I don't recall of the top of my head what it should be cold or warm. I think the Bentley has those numbers, otherwise we have discussed it before.
T77911S may have got it right, so concentrate on the AAV. The high RPM leads me to believe that you have an internal air leak, via the AAV or AAR. So check the AAV and you might as well clean the AAR. The AAR closes by action of a bi-metal, so heat from the electric heater or the engine will cause it to close.
The Bentley does a good job of describing how these some of these things work, so check it. Print out the electric diagram in my signature (in color) and keep it in your glove box. It is a great tech reference to have. Make notes on it for the resistance of the components (thermo time switch and AAR...hmm maybe I should have done that on my
)