AubreyDawn

As stated 2002 WJ with a 4.7, 262,000 miles. It has been running rich for the last 4 weeks. My gas mileage is half of what it was and a V8 ain't cheap to start with! Idle is a little rough and stays at 650 rpms. A week ago I started it up and it revved to 2500 rpms and dropped to 650 rpms about 5 or 6 times, then leveled out. My biggest issue/concern is the black oil.

And before anyone on here gives me a lecture, I don't need one. I know how to watch my oil and pay attention to my vehicle. Oil gets dirty. I get it.

I run synthetic and it is generally still clearish when I get my oil changed. This time my oil was black when I went to get it changed and BLACK THE NEXT MORNING.
(My friend owns the place that changed my oil, so yes they changed it)
I'm very concerned and need to know how to start trouble shooting. I've read about compression tests, piston rings, IACV and a few others. What I need to know is what is the usual cause of oil going black over night??? When the previous oil change went 3000 miles before I changed it CLEAR AS F@#$.... Also, I can smell it running rich. Very strong odor.

Thanks in advance!