P2187 And P2189 Codes

The Check Engine light on my 2005 MPV with 89K miles, has been coming on. I'm getting either P2187 (System too lean at idle bank 1) or P2189 (System too lean at idle bank 2) codes.

I removed the MAFS and sprayed it with electronic contact cleaner, but that did not resolve it.

The CE light sometimes turns off by itself, and it is more likely to come back on when the weather is wet. That leads me to think there may be a bad contact somewhere, but if its not the MAFS, what can it be?

The engine runs fine; idling, cold-start, acceleration, etc are fine.

I'm looking for suggestions on what can be causing the codes before I go to the dealer. Thanks!