I can't say this has worked out to be a huge problem perse,,, but on my 2002 XK8 if in "P" I rev the engine up to about 3 - 3.5 or 4 RPMs,,,, then I let off the gas completely the RPMs fall and - STALL! Predictably. She starts right back up like nothing happened.

What's up with that?

Otherwise, she runs beautifully... Since owning her over the last 4+ years she has always brought me home, never spent a dime on more than elective and routine maintenance - 210k on the counter...

What are the idle fuel trims?

Try cleaning the throttle body and butterfly. A buildup of gunk can make the butterfly stick when it rapidly closes from wide open. But don't spray cleaner in the throttle body, use a rag and small stick.

I have, but it's been a while... And will again. It doesn't happen everytime,,, but it's like I'll rev the engine in Park and with a sudden let of of the gas watching the tach and the RPMs drop well beyond normal idle (about 650 to 670) and not always recover, well... Sometimes stalling.

I've never checked the trims, can't say that I rightly understand the concept (which is true for a lot of things). I do have an obd and will go into the settings/functioning and try and figure out how to get readings... Then report back. Right now the OBD is with the XKR that I've been monkeying with. But I'll get to it in the next days.

Thank you both!

Was the Check Engine Light (CEL) on or not? Check for current codes and any previous codes stored in history. One subtle problem that doesn't generate a code, that you can quickly & easily cross off your list, is a vacuum leak. This affects idle moreso than driving. Sparingly spray starting fluid around the hoses, intake areas and in particular, the hose running to the brake booster, and listen for a rise in idle.

I'd have to explore a couple of other things that affect idle like PCV and EGR valves, too. These can produce vacuum leaks not detectable with starting fluid.

While you have the ODB tester hooked up, you'll have a handful of gauges in the palm of your hand. You can glance at things like voltages, fuel pressure, vacuum, timing, rpm, engine load*, throttle position,temperatures, fuel trims.... stuff you can get familiar with. Back in the good old days with carburetors and points, one of the first gauges to grab was the vacuum gauge. Now that we have one as standard equipment, no one talks about it.

*an internal or external parasitic load, from engine, accessories or transmission, can drag the engine down faster than ECM feedback can compensate for.