I have a 2001 s type 3.0 v6, at last year's service the garage changed the 3 hidden spark plugs located beneath the manifold, they tend not to change these at yearly service because of the work involved , since then when I have driven for approx 1 hour, the engine jerks on acceleration i have had 2 jaguar technicians look at it ,and of course it doesn't happen when they carry out a road test, it seems to be worse when the air con is on, the car has a full history , I have owned it for 6 years ,and it has only 55 thousand miles, any advice would be very much appreciated .
Ditto Mike's comments, I had this on a 99, V6 Petrol, not only was it a cracked insulator on a Ford marked Spark Plug which even I could see when I decided to have a look for myself, these were clearly the originals in since the engine was built by Ford, under the manifold despite full annual services being carried out which I paid for in good faith for 5 years, the "on spark plug" coils were defective also. My solution was new plugs and "on spark plug coils"under the manifold. All mis-firing eliminated.
2005:-S Type V 6, 2.7D
2009:-XF 3.0D V6 Premium Luxury