Originally Posted by mpich
So what should I get them to check?
As Willwren suggested, you could reset the PCM by disconnecting the battery for half an hour though I'm not sure if this will clear the codes. If it doesn't, go to the dealer and have them clear the codes with a Tech II.
What we want to see next is whether the codes you previously experienced will be set again.
An oil covered MAF is a funny situation, in that state it cannot read the airflow correctly and under reports the Grams/Second of airflow to the PCM. This situation does not set an SES light but causes a cascade of problems. The PCM commands fuel based on the air it thinks is enetering the cylinders, obviously this is picked up by the O2 sensor as being too lean but in all likelyhood the PCM is unable to add sufficient fuel (it can add up to 20%) to bring your Air/Fuel Ratio into line.
I've seen this problem a few times previously and when you look at the MAF it doesn't look dirty but it takes very oil to inhibit its' ability to read airflow.
If your car is performing better after the MAF cleaning then that'* great. But now you must make sure that was the problem and that it'* not something else. You must have the codes in the PCM cleared and pay attention that they are not set again. If they're not set...then you're all set
...but if they set again you'll have to dig deeper.
Hope it goes well.