I have a 2000 S-type 3.0 that has had miss fire issues along with loss of power and gas mileage. It has 104,000 miles. I have replaced the cop's, o2 sensors, upper & lower intake manifold gaskets. I am using Pulsar Pulstar plugs. I recently took the fuel injectors out and had them re-done. After fighting issues with the spark plug tube gaskets leaking oil into the spark plug wells and shorting the coils I think I have that licked. The missing is gone for the most part but I'm getting a P0430 code and I want to rule out a vacuum leak before I start looking into more expensive problems. I've tried the cigar trick to try to locate a leak but I could not find anything. Any suggestions?

 

Have you replaced both of the hoses which tend to perish and leak at their elbow?

You can check (long term) fuel trims using OBD live data. If there's a leak they'll change markedly between idle & 2500rpm. Much cheaper than swapping parts and hoping.

Lots of threads about this...

 

This is a common leak point on your model:

https://www.jaguarforums.com/forum/s...um-leak-67197/

Sorry, couldn't find a link to a the thread with a picture, but I know there is one on here, somewhere. This one has the p/n though.

 

Here is the thread that aholbro mentioned:

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