I own an '01 S-Type and have had to many problems to list, however 3 months ago mine started riding rough, the check engine light actually started blinking and it shook pretty bad especially at stop lights (although it didn't shut off) I drove it straight to the shop and they said it was a bad ignition coil (coil #4) - $135 total and it ran fine. 2 months later coil #5 went. I was advised that if you take it to the dealer they will replace all 6 ignition coils at once charging you over $1,000. They are only about $60 a part stores. Good Luck I'm getting rid of my Jag this week! What a pain in the neck beauty!

Does it do this all the time? if its only when you start the car after say a long cold night there could be a problem with ur automatic choke or your timing could be out.