Since I could not find any good threads on TW for the problem that I was having, found one good one on XRU though, I thought I would post one here.
Note that I have fixed the problem, but wanted to provide some detail in case someone else ran into it.
About 6 weeks ago, my truck threw a MIL (09 4.0 DCSB), code P0101 -
Mass Air Flow (MAF) Circuit Range/Performance Problem. I have a URD CAI and a MAF Cali that I added last Sept and Jan respectively, so I figured it had something to do with those, but wasn't entirely sure if, much less which on. I reset the codes, and drove for about a week or 2. MIL came back with the 101, plus P0172 and P0175 - System too rich (bank 1 and bank 2).
I reset those codes, then added Xgauges to my Scangauge to readout the fuel trims, long and short, the MAF sensor, and A/F ratio. The LTFT was running about -10-15, with the STFT running about the same. these are high, but not code setting high. AFR looked normal, and the MAF reading, from what I could research, looked within range.
Drove it with these monitors for another couple of weeks, with the settings in the ranges above, then one day the LT and ST fuel trims went to -25-40, and the AFR was running 16-17. MIL didn't set, but a pending 101, 172 and 175 were set. After turning off and back on, all readings returned to the "normal" above.
I did some searching on the codes + Tacoma + URD CAI and found a thread on XRU talking about this same set of symptoms, but the occurances were more often. Solution suggested there was a bad URD CAI MAF extension problem (bad connection). Wiggling wires on the XRU problem seemed to change the trims and MAF reading. Wiggling the MAF connections on mine didn't seem to affect the readings at all, but they had returned to "normal".
Reset the codes again and drove for a couple of weeks. One day the readings went wild again and I was able to pull over and wiggle the MAF extension, this time a wiggle at the engine-side extension caused the idle to burble a bit and readings returned to "normal". Aha, found you...
Up until then I wasn't sure if it was the MAF extension or the MAF Cali that had a bad connection. Was hoping for the CAI since that was easier to redo.
I pulled the connections on the MAF extension, engine-side, and resoldered and shrink tubed. After driving for a couple of miles, the fuel trims returned to small single digits, +/-3-4, and have stayed there since. Pretty sure I have it, but it hasn't been a couple of weeks yet.
When I was re-doing the connections, all the soldered connections looked good and passed the pull-apart test, so not at all sure which one, or more, was bad.
So, those with the URD CAI, it is possible to think all connections are good, when there may be a questionable connection there. Only looking at the fuel trims was I able to find some anomolies. AFR was helpful, but by itself, not so good, and the MAF reading also was helpful, but by itself hard to diagnose.