91 XJS 5.3L Idles too high when cold
 

It idles at 1200 - 1500 rpm, depending on how cold it is. If I screw it in, it idles too slow when it gets hot and the engine dies. The AAV (Auxillary air valve) is supposed to compensate for temp. when it warms up, but it's compensating too much.
There are at least 3 part numbers for these, and my VIN ends in 179493, so from the page at:
Extra Air Valve-5.3 Litre - Parts For XJS from (V)139052 to (V)179736 | Jaguar Heritage Parts UK,
there are 5 part numbers for the AAV: A - EAC4438, B - EAC2273 and EBC1198, C - EAC2273, D - EAC2273, F - EAC4438, G - EAC2273.

Is this a common problem, which AAV valve should I use, and how do you troubleshoot it?

Does the idle change once the car has warmed up?

IOW, if you have a cold idle of 1200-1500rpm, what is the idle after the engine reaches operating temp?

It idles between 600 - 900 when it's warm.

Then it sounds like the AAV is actually doing it's job, so that's not the problem.

Why do you think the idle is too high when cold?

Or is the issue that the idle fluctuates?

Um, 1200 to 1500 hundred when cold and 600 to 800 when warm is called "normal operation"

Thanks, I didn't know that it was "normal" for it to idle so high when cold.

The "cold idle" can be reduced.

You MUST understand how that AAV works, or you will stuff it up.

The adjusting bolt on the side is the HOT idle adjustment, and should not be played with until the engine is at operating temp, at which time that AAV should have closed the inlet port 100%.

Have a read of the attachment, and I think it will clear up a lot of the mystery.

Attachment 126209

Very Useful 'Grant' Cheers!

During the Winter Layup (6 months!) I Started her up a few times, just to keep her fresh and ready to go, where one day She developed a 'Hunting Problem'

Where the Engine would 'die' and then recover and although She never cut out, She came quite close.

I was reading in one of 'Greg's Posts' that this was almost certainly down to a Sticking AAV but fortunately She managed to cure herself.

Though if it comes back with a vengeance, then your PDF on how to fix it, is going to be invaluable.

Having got her Tax renewed, I was hoping to do the first run out of the year but unfortunately, it is chucking it down with rain. 'bummer!'