Fast Idle Experiment

As we XJ-S owners seem to have the most reliable Jags on the planet, judging by the lack of posts, I thought I would throw this out for general amusement.When I first bought my car, the fast (Cold) idle was all over the place- sometimes high, sometimes low.It took me a while to learn where all the vacuum lines went, and there were SO many controls- AAV, SAV, vacuum solenoid switch, thermal vacuum valve, diverter valve, dump valve, and on and on.I have made some changes because some of the control valves just did not work, gummed up, open circuit, etc.
The AAV was replaced by the PO at great expense two years before I got the car, and I’ve never been very happy with it. I took it off the car, did the boil test, and it seemed to function well enough, and it does a good job of controlling the idle speed, but that’s about it. Now that winter is here, and I have all this time on my hands, I thought maybe I could come up with something better. I saw Bernard Embden’s manual heater valve fast idle scheme, but didn’t want to drill through my firewall to run a cable, so this is what I’m going to try. The photo shows a vacuum heater valve, normally closed. I’m going to hook it up to my unused thermal vacuum valve on the RHS water rail. The garden hose shut-off will be used to control airflow, and everything will be teed into the vacuum line that connects the SAV to below the “A” bank intake manifold. After a couple of adjustments, I hope to have an automatic fast idle control. Needless to say, incoming air will be filtered. Is it spring yet? All of this hardware will hide below the “A” Bank airbox, BTW.

deleted. I figured out the details of your car are obvious once you click on your avatar.