What is this blue thing? It has a vacuum line going to it. Lotta junk up behind throttle pedestal!
Greg,
That is your Throttle Control Valve (JLM473). It senses high throttle setting via vacuum and enriches the mixture to prevent burned pistons. I see it as a redundant sensor to the Throttle Switch (C35509) on the pedestal that works differently but for the same purpose. It is very important in preventing burned pistons.
I recommend that you get a Jaguar XJ-S Parts Catalogue to help solve some of your parts mysteries. I purchased a hard copy of “RTC9900CA January 1987 on” on eBay about 13 years ago and use it regularly when working on my wife’s 1990 XJ-S convertible or trying to source the correct parts.
BTW, if you search the archives for “Throttle Control Valve” or “JLM473” you will likely find a few discussions about this part, including how to test it to find out if it still works, and an aftermarket replacement just in case it doesn’t work.
Paul
Thanks Paul! 