As I've mentioned before, and as we all know, forums are often a mixed blessing. With the Jag stalling off the throttle and providing sporadic moments of terror, a little research produced a long list of potential problems and few certain fixes. The main positive (I think) was that this was a common issue.
Arranging the various jobs by price in ascending order and starting at the free end, I showed my list to colleague Lewis Kingston, who instantly suggested a good clean of the throttle body was the best place to begin. With that, we ventured into the car park.
Armed with some silicon spray, contact cleaner and old rags, we lifted the bonnet, undid the hose clips securing the air flow meter and lifted it out. We were greeted by a distinctly oily throttle opening, which was dripping the stuff onto the throttle position sensor directly below.
After giving the throttle opening a good spray with carb and intake cleaner and wiping it clean, we unclipped every sensor we could find and gave each a good spray with contact cleaner and a decent dry, before reattaching.
Next was the throttle cable. When left for a few days, the Jag's throttle tends to stick around halfway, but pressing through it loosens everything up. It has always been a little slack, too, but I'd forgiven it that after its 150,000 miles of service.