Well, the new MAF arrived today (gotta hand it to Pacific BMW...). I also finally got around to buying an OBDII code reader at lunch today, thanks to the prodding of Mr.Paddle.Shift, and read out the codes that were lighting my Service Engine Soon indicator.

(Those of you who are familiar with my modification exploits might wonder how I went this long without a scan tool, and you'd be on solid ground with your incredulity; I can't explain myself, so I won't try )

Here's what's going on:

P0171, 174: Running lean, banks 1 and 2

P0313: Misfire (I know what caused this, so it can be ignored)

P0369: Camshaft position sensor "B" circuit intermittent (this one has me a little concerned, and it showed up again right after I cleared the diag codes out, so needs more investigation; hope it doesn't have anything to do with the engine cleaning I did before the 'fest )

P1191, 1193: Pre and post cat fuel trim problem

So, the codes that are really meaningful here, 171,174,1191, and 1193, are all consistent with a contaminated MAF. If some oil has gotten on the thin-film/wire in the MAF, it would cause the sensor to indicate less airflow than is actually occurring, resulting in a lean mixture.

I cleared the codes (and the MIL/SES light), and plan to run with my existing MAF until I get an MIL again, then check the codes. If the same, I'll clear it again and go one more round to see what turns up. If I get the same basic faults, I'll swap the MAF, clear the codes, and then see what happens.

I'm betting the MAF's the problem, but I can't know for sure until I disassemble it, which from what I can tell will be a destructive project.

If not, my next step is to invest $122 in some OBDII scanning software for my laptop so I can monitor and record engine operating parameters in real time while driving, and catch the failure. Then I can get a better idea of what's going on. I plan to purchase a copy of Vehicle Explorer, which looks like a pretty decent tool. For the technically minded, you should click the embedded link and check it out.