Just wanted to report on a recent issue I had with my 2000 4runner. This site is awesome and there are lots of knowledge people here and I just wanted to give back.

I use K&N airfilters and these frequently gum up mass airflow sensors which I didnt realize until I started getting a PO171 code. I took off the maf (on the airbox outlet) and cleaned the two tiny wires inside the tube of the maf with a spray of maf cleaner and prob solved! I could see the gunk on the wires before hand and after cleaning they should be clean down to the metal. There should also be a little plastic sleeve on the wires - leave those. After cleaning - no more PO171 code. Just wanted to let people know about this. The info is in these forums but not so easy to find.