Had a water pump failure on a 1998 E 320, 208k mi. In the process of the repair, the airbox was removed, and the MAF was disconnected to move the snorkel out of the way. Upon conclusion of repair, the CEL showed up indicating a malfunctioning MAF. Car runs normally. No idle issues, no hesitation, stinky exhaust, or bad mileage. Tried a junkyard MAF, and also a new BOSCH unit. Every time the code is cleared, the light comes back on within several miles.
OTC scanner in DATA VIEW mode shows the fuel trims on each bank are 15.xxx and 17.xxx. MAF data shows about .33 lb/min at idle, and as much as 8.xx on the road (depending on how aggressive I drive). These are essentially the same readings for all three MAFs I have tried.

I have not inspected the snorkel feeding the throttle body for cracks or leaks. Everything else on the scanner seems ok. What else should I be checking? Wiring to the sensor seems fine if all three behave the same. I'm stumped. If anyone has seen this before, or has any info to add, I would appreciate it.
Thanks!

having done a bunch of those pumps in almost every body, i don't see why the mass meter gets involved from the rear of the intake.

IF it's a v6, that amm can be tricky to seat right. you post data, what codes?

What code are you getting?

First off, thanks for the replies. I am not a mechanic by trade. Just a guy who has always worked on my own vehicles. I appreciate the help.
The code was P0105. Engine is the V6. As I said, I could clear the CEL, but no matter which of the three MAFs I tried, it would return within a few miles. Reading up on this failure, vacuum leaks seemed to be the main cause. I looked over the intake snorkel for cracks or other trauma, but it was in good shape. Moving up to the front of the engine, I found that I had damaged one of the vacuum lines that run from the base of the intake manifold to (I believe) the EGR solenoid. It happened during the water pump repair. These lines were old and gummy, so I replaced all that I could reach without pulling parts off the engine. There are only two i couldn't reach, and they looked better than the ones I replaced. I will keep my eye on them.
At this point, I have test driven about 30 min, and so far so good. LT fuel trims have crept back down from 17.XX to 12.XX on each bank. I expect to see them below 10% in a day or so if all goes well.
Confidence is high. Wish i didn't buy a brand new MAF so soon. Let this be a lesson for others!

Thanks again.
Craig

Attached Thumbnails

 

Your code is not about the maf but the map sensor, its the small square sensor near the oil filter and has one vacuum tube connected to it.

It also acts as baro sensor right before engine startup.

Your fuel trims being positive also mean that you have a vacuum leak..

That broken piece you circled is the map sensor.

Yes, that is indeed the MAP in the red circle. The component to the left has to do with EGR. My mistake. I drove it more last night, and its behaving normally. I'll put the scan tool back in line and verify the LTFTs have returned to normal. Appreciate you looking in on me! Be well- Craig

The map sensor is also used for egr activity confirmation by the ecu, its not just for egr though,

Before start, its used as the barometer by the ecu and after start it is used in conjunction with the MAF sensor to create a correct engine torque/load signal which is used by the engine ecu and also used by the tcu and esp.

Replace it, its pretty cheap, however if you find that the vacuum hoses are perished, toyota dealers sell genuine hose in 1m lengths, and if the small vacuum chamber in the manifold isnt holding vacuum you will need to install an external vacuum tank or a new intake manifold.

Good information. Thanks! I will look into the Toyota vacuum line. My stash is all in fraction sizes. I agree on how the sensors all contribute to best establish the ideal fuel curve each second, but did not know about the baro info for startup. Interesting. Again, I appreciate the help!

And so far, the vacuum leaks have been solved. I was hoping to see a vacuum reading on the scan tool, but there was no category for that on mine. I can "T" a line on the front and do a manual check. I would expect to see something near 20" mercury at idle?

Thats odd, I can see a MAP sensor reading on a M112 on a generic scan tool and even on a cheapie TorquePro and android.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

You're probably right...When I see measurements in metric specs, I tend to gloss over them...Next time i hook up the scan tool, I'll switch it over to English/US units and probably see it straight away.