Unplug the OS sensor connector, unlplug battery for a few minutes, it should
reset the ECU in safe mode. Try the van back
If the problem is gone, you know what to do.

Spay some WD-40 on plug wire and any electrical wire subject to rain or
water including the AFM wire. Also check the ECU blue Temp sender wiring.
Try the van in rain.

Cheers, Ben
http://www3.sympatico.ca/huotx/engine1.htm