March 20, 2009
G70 Mass Air Flow (MAF) and MAF screen function
As far as I can tell, the mass air flow sensor (MAF) for the ABY S2 is the same as that for the RR Urq, the 3B S2 and 200 20vt and the UrS4 and UrS6 (all same PN 034 133 471 K). The RS2 MAF is similar but different (wider opening screens) (PN 034 133 471 N). (See photo below: 471K on he left, RS2 471N on the right). In both cases, when the engine is shut off, the ECU sends a current to the MAF hotwire that is enough to burn off the crud that has accumulated. (NOTE: PN update the 471N RS2 MAF is the same as a 944 turbo MAF PN 951.606.125.02 (also Bosch 0 280 213 017))
Airflow of the RS2 MAF is superior to the 471K, as pointed out in a post by Manx:
Click here to see what Manx found -
AAN Mass Air Flow (MAF) sender on left, RS2 on right.
Back on Feb.22, 2004 “manx” posted:
“I don’t show it but the RS2 is less restrictive approx 2in h20 vs. 2.9 for the stock maf, I haven’t checked the stock one without the screens, but suspect that you would need to remove both to get it the the RS2′s backpressure. Other then that they are basically the same, just a few hp lost trying to get the same flow out of the S4 unit, at least up to 180cfm. Anyone got numbers off up to 600cfm, from a larger flow bench. I am currently doing data aquisition on MAF voltage vs. RPM on my car to get a better idea of the map for the RS2.”
More general info is available in the Autospeed negative boost article.
Removing the inlet screen on the 471K will improve air flow but could lead to turbulence across the hot wire (and therefore bad signals). Not too much is said about the rear 471K screen.
The electrical signals from the 471K and the RS2 MAFs are similar. Close enough that, in the last few years, tuners have been tuning using the 471K, even with RS2 and above turbos. BUT remember, the airflow is still less with the 471K with the screens intact.
Here is what Cody Payne found out about the 471K and RS2 471N output voltages:
The voltages are very very close to one another 
The MAF connector sometimes develops some corrosion and may need to be cleaned and Stabilant 22 added (to keep the corrosion at bay). If there is more trouble, you might want to replace the connector.
As with all Audi electrical devices, the power is brought to the device in a female flat pin connector that mates up (no pun intended) with the male pins that stick out of the device that is to be powered, in this case, the MAF. In the case of the MAF, it’s a flat six pin female connector or “terminal housing” in Audispeak.
The PN for this six pin connector was originally 022 906 233 A. However, at some point, it was dropped and replaced by 025 906 238 B. The female pins for this connector typically come two on a yellow covered pig tail wire. The PN for these female connectors is 000 979 133 or 133A for the 1 mm wide pins or 225 or 225 A for the 2.5 mm wide pins. The “A” is for the gold-plated version (slightly more costly but likely the ones you want if corrosion is a problem).
NOTE: Another MAF problem is sometimes the male pins of the MAF miss the “target” on the female pins and end up pushing the female pins backwards, out of the harness MAF connector. If that is the case, all sorts of wierd missing happens (poor connection) and maybe even a 4411 code (i.e. injector No. 1 fault). The solution is to clean the connection (male and female pins) and then after reconnecting, pushing the female pins individiually, from the back of the connector towards the MAF to make sure they are properly mated with the male pins.
Hope that helps somebody.