I have a hot no start/slight stumble problem with the 2000 XJ8 and am looking at potential culprits.
I was surprised to see that the little ole fuel pressure regulator JLM 21358 is $399!
The same part is also SAAB 12801657 which can be picked up for $35 (nonOEM). It fits 2003-2006 SAAB 9-3s.

 

Did you take pictures ?? love seeing pictures

 

Are you sure it's not the fuel pump? That can cause the symptoms you describe and if the car has over 100K on the original it could be the culprit.

-Mike