You can hope for faulty O2 sensors or a vacuum leak but it's probably a bad cat(s).
Tap your brake. It suspends the cruise control until you hit resume
Back left hand side in the trunk up a little from the floor under carpet your changer is there
clutch slippingJaguar has a software upgrade for the Engine & Transmission computer module. Costs too much but will probably help. Also, one or more of the upstream O2 sensors on may be faulty, especially if you are getting a check engine light.