There are a zillion posts on AJ16 high idle problems.
Does a "Comprehensive guide to high idle problems" or similar exist?
I started to work on one but figured I should see if it's already been done.

 

How many endings are there?

Usually it's the TPS or the IACV or a vacuum leak. I'm not even sure the oxygen sensors affect idle that way.

 

I would definitely find it helpful.

I'm dealing with an issue where it idles high when put back into Park or Neutral after a drive, (it is normal every other time eg. starting, driving etc).
I've tried searching the forums but perhaps have not stumbled across the right thread yet.

 

Also problems with ECU (fuel trims etc.) that require a PDU to fix.
It seems like quite a few people go through the TPS, IACV setups and still have the problem.

Look at it from the perspective of a new owner with a high idle. A search on XJS high idle came up with "About 237,000 results".
Where to start?

I was thinking of a single document explaining how the idle is controlled including diagnostic and troubleshooting procedures.
It would be a combination of info from the Engine Management System Manual, Service Manual, Maintenance Manual, etc.
If nothing else it will give me something to work on over the winter!

 

PDU can reset long term fuel trims, but that's about it. Resetting the LTFT won't have any effect on anything. It's simply a long average of the short term trims.

(I have a PDU)

There are 237,000 results because it's a common problem. The solutions are few.

I look forward to seeing what you put together, I'll be happy to help.

 

I stand corrected. Look at my post #21

​​​​​​https://www.jaguarforums.com/forum/x...-237002/page2/

 

Thanks for the offer to help. This will take me some time. A rainy/snowy day project.
I'll send you something when I actually have something put together..
It would be great if you would go over it and check, edit, correct, add to, etc.

Quite some time ago we talked about getting together to do a reset on my '96 4.0.
That didn't work out but maybe someday . . .

 

The PCValve on the back of the driver's air filter housing can be a culprit too, as can a sticking throttle or cruise cable.

 

The AJ16 does not have a PCV and a sticky throttle cable is not a common issue. The x300 cars might use a return spring on the throttle body, but I'm not sure I've seen an XJS require one.

-V