I put in the "old" MAF. Car ran fine for a few days. Yesterday, I got the rough idle again. I checked the codes, and show misfires on 4 of the 6 cylinders. I had read somewhere that if you unplug the MAF, the car will adjust, so I did that to see if the rough idle went away. Nope.
I happened to have the DTC code reader hooked up at the time, so I looked at the signals from the MAF. Here's what's odd - the inlet air temperature showed -70 (and 95 when the MAF was connected), which is what I expected. However, the air flow showed EXACTLY THE SAME, even changing with engine RPM, whether the MAF was connected or not!
I'm starting to wonder if I have a wiring problem. I plan to check the wiring with a voltmeter over the weeked to see if I have a short.
I also figured out what the MAF should read, based on this article
http://www.installuniversity.com/install_university/installu_articles/volumetric_efficiency/ve_computation_9.012000.htm
Based on 80% volumetric efficiency, I made this table:
Speed Estimated
rpm lb/min
0 0.0
1000 3.2
2000 6.5
3000 9.7
4000 13.0
5000 16.2
6000 19.4
7000 22.7
This will let me know if the numbers I see are reasonable.