Hey guys - trying to figure out the vacuum issue (P0171/0174) and I took off the MAF to clean, and noticed the sensor is missing when compared to others from Rockauto replacement MAF. So, what gives?

Most of them are inside the sensor these days, there are very few left with the sensor outside the housing anymore. The circuits are designed with compensation for any change in apparent airflow caused by the buried location.

So the one on the bottom has the sensor inside...hmm. Ok. Just weird that mine looks like the bottom one but still has the two spots to hold the sensor.

Notice everything is similar except the foot, which is a separate plastic part. No doubt the manufacturer puts several different parts with varying circuits and varying ranges of measure into that same housing, all similar in the connector they accept and the hole they fit into, but different in electrical capabilities. You wouldn't use the same MAF in a 1.6 Versa as you would in a 5.6 Titan, but the hole and the connector are identical.