P0102 and P0325 Fault Codes on 1997 Subaru Impreza Outback Sport: Diagnosis and Fix

I own a 1997 Subaru Impreza Outback Sport with an automatic transmission and no modifications. The car has been driven regularly in New York City, where humidity levels are high. The check engine light (CEL) came on intermittently, especially during humid weather. Initially, I assumed it was due to a knock sensor issue — which triggered the P0325 code (Knock Sensor 1 Circuit Malfunction). After a partial tune-up (spark plugs, wires, oil filter, and oil), I tried cleaning the knock sensor, but the problem persisted. Recently, the car stalled multiple times in succession. I took it to AutoZone, where they confirmed both P0325 and a new code: P0102 — Mass Air Flow (MAF) Sensor Circuit Low Input. I researched the service manual using BitTorrent and followed troubleshooting steps. According to step 2, I tested the power supply to the MAF sensor with a voltmeter. The reading was only 0.03 volts instead of the expected 10V+. I also directly touched the meter leads to the MAF connector terminals — same result. P0102 is commonly attributed to a faulty MAF sensor, though AutoZone's display shows 'MAP' as well. This discrepancy may be due to older diagnostic systems or terminology differences between MAP and MAF in some models. I’ve verified that the wiring appears intact and there are no visible signs of damage. I have not found any dedicated fuses for the MAF sensor, which raises concerns about power delivery. The main relay (located behind the instrument panel, below the fuel pump relay) is suspected as a potential source — testing continuity between pin 3 of the relay and pin 1 of the MAF sensor may reveal a broken wire or failing relay. After further investigation, I discovered that my air filter had not been replaced in years. It was pitch black due to heavy use. I suspect this clogged intake may have damaged the MAF sensor over time — explaining intermittent readings and stalling behavior. I replaced the MAF sensor (found for $50 on eBay), cleared the codes, and the issue has not returned after one week of normal driving. Note: The OBD-II database does not list stalling as a symptom of a faulty MAF in most vehicles. However, the 1997 Subaru service manual explicitly states that a bad MAF can cause engine stalling — which matches my experience. I’m sharing this to help others with similar issues on older Subarus. If your car stalls and restarts immediately, especially in humid conditions, consider checking the MAF sensor or air intake filter.