So, I inspected the intake boot again, looks totally fine on every part I can see. I also checked the vacuum on the oil cap, it was strong. I was impressed. I didn't know there would be any suction there.
I decided to start over, and take a look at the MAF again. That is the logical place to start, and when this first happened the first thing I did was get out the MAF cleaner and follow the instructions. Today, looking at the MAF, I saw that there was some rust, or corrosion on the actual sensor tip. I took off the cover and gave it a real cleaning. I used the spray, but also rubbed it with a cloth and a small knife to get the residue off. Yes, we are told how delicate this thing is, but I figure that with that residue I might buy a new one anyway.
But I cleaned it up, we'll see if that fixes everything.
Past ownership: 1987 325is, 1988 325i, 1995 325is, 1996 325i Convertible, 1994 325is black coupe (which I miss).
Current ownership: 2002 330i Sedan with some cool DINAN upgrades, 2006 X3 3.0i