2004 XC90 Surging Idle & engine dies

[APCalifornia]

Hello,
I've been searching Volvo forums while I step through the problem I've got: about a month ago my 2.5 T5 starting surging lightly at idle. Within a week it was really rough and would die after giving it a little gas. My local mechanic didn't give me the actual codes, but said it was something in the fuel mixture, and was likely the MAF. After discussing this with the previous owner & his brother who both still have the same car, they suggested also checking the PCV system, especial the oil trap, although I did not have any smoke coming out of the dipstick tube. I also read about cleaning the ETM.
So, starting with the ETM project, I cleaned it up really well. Since they told me about the oil trap at about this point, I just moved to that step: unfortunately even though I read to be careful around the tubing, I snapped the thin hard plastic tube that comes from the top of the oil trap to the hollow bolt (Banjo bolt?). The oil trap was definitely clogged, the 1½" port from the engine block to the trap was halfway filled with sludge, the smaller port at the bottom of the trap to the block was completely blocked with sludge. I replaced 3 hoses and the plastic tube, all of the clamps, and reassembled everything.
The fuel injectors look very clean, but I don't know how to test them so any one of them could be defective.
I tried unplugging the MAF, but nothing changed. Not having the instrument or procedure to test the sensor, I bought a new one from Delphi and installed it. I've read about the voltages at each pin of the connector, and mine seem to fall in the ranges.
Still has the aggressive surge at idle and will die if I give it a little gas and suddenly take my foot off the pedal.
Question: if I disconnect the battery, does that clear the CEL and change anything else in the "computer"? Are there any other steps I can take?

[APCalifornia]

UPDATE: Yes, disconnecting the battery for 30 sec. does clear the "computer" - after doing this, the surging and engine issue cleared immediately.
Next issue that showed up was "No Oil Pressure - Stop Engine"; I knew I had enough oil, but the pressure warning got me on this site again. Found a few things to work on, and the easiest was to add an oil/engine cleaner to the crankcase and complete an oil change. Once that was done, and the battery disconnected again, the warning went away and everything is good again. Must say thanks to all the posters from all the years back that I could find in my searches.