Rpm dropping way below idle when revving

Hi so I have a question I took the car out for a regular drive may have pushed it a bit hitting around 90-100 on the highway engine was running fine smoking more then usual but it’s always been a bit of a leaker when it comes to oil once I slowed down and went to fill it the engine seemed to be running higher then it was clocking in at the dash but after a second would regain it’s normal sound but once I got it home and was sitting at idle in the driveway I revved it a few times and now the rpm’s drop almost to zero and recover after a second and it’s leaking way more oil then usual I was just wondering if anyone had any insight on this problem and it definitely isn’t moving out of the garage until it can either get looked at or I get some insight to the problem thank you to add on it’s the 1986 xjs with the 5.3 L V12

Lets start with the model year and engine?

Sorry the years 1986 and it’s the 5.3 L V12

Where’s the oil
Leaking from?

I haven’t fully looked but it leaks very close to the oil pan and I know these cars usually leak but it’s now a ridiculous volume of oil I thinks it’s either a connection between the engine and the pan.

Have that fixed and maybe that fixes a vacuum leak which causes your revs to drop unusually.

The engine doesn’t notice 90-100, if it did it would actually help burn off junk and help with oil consumption as well.
I drive my cars fast and oil consumption goes down a few weeks into ownership (for good, and on new oil)

That what I thought cause if anything after u ran it hard the engine sounded the best it has and it was running smoothly until I sat it in idle and that when I started noticing that.