A quick question on my NA V8 5.0 non-supercharged 2011 XJ. After heavy acceleration with high RPMs when I let off the gas the revs go down very slowly. There's no immediate drop off when I take my foot off the gas and it kind of chases itself down. I tried searching around but I couldn't find any information on this at all. Is this a normal thing or feature?

 

It certainly doesn't sound normal at all to me. I would get the car checked out asap, because one day the revs might not even reduce at all. The throttle is a "Fly-by-Wire" system, with no physical connection between throttle pedal and throttle body.

 

I agree with Fraser.

 

Check fuel trims as it may well be an air leak.