One problem related to engine has been reported for the 1998 Jaguar Vanden Plas. The most recently reported issues are listed below.
Engine will shut off while driving. This problem has happened to my wife and myself while driving many times (>20) but fortunately most of the times she was on city streets where it wasn't much of a problem to get over to the side of the road. The greatest problems have occurred while my wife was driving at speed limit (65 mph) on freeways in the fast lanes. This caused her to almost be involved in a traffic accident as she tried to pull over to the side of the road with no power in heavy traffic conditions. I think this is a major safety issue. According to the dealership (bauer Jaguar in santa ana, CA), the problem is caused by a closure of the throttle body plate when the unit goes into a self-cleaning mode. The dealership has made a change in throttle body plate stop so that it will not close all the way when it goes into this self-cleaning mode. The problem has not occurred again since the dealership applied this change but I have a greater concern for other people who might encounter this problem in the future.