Captain_Slow

Over last summer I noticed the idle was stumbling a bit and acceleration had a bit of hesitation. At Frenzy in the hotel parking lot Stan and others noticed it smelled rich (so much so we didn't stand behind the car long). The discussion lead to possibly a failing MAF or O2 sensor. I started Googling a bit and read that a dirty MAF can cause a rich mixture. I picked up some CRC MAF cleaner and gave it a go. So glad I did. I noticed a difference as soon as the engine started. The idle was much smoother during warm up, and it remained stable when the rpm settled down to 600. But the most notable improvement was no more stumble and hesitation when mashing the pedal. Even easing on to the gas pedal and gradually giving it more was impressively smooth and strong.

This was the first time I've cleaned the MAF. I was ready to go for a rebuilt MAF and it's likely still a good idea given the age, but I think I'll wait until cleaning doesn't yield the same results, or the more obvious signs of a dead MAF.

It was also nice to see that everything was still nice and tidy under the air cleaner 2 years after doing the top end refresh.

Mrmerlin

Jon I would suggest that you have the MAF rebuilt now.
NOTE since you had an issue with it,
its quite possible it could fail soon

M. Requin

Hmmm... Hawaii, cybertruck, MAF cleaner - am I seeing a pattern here??

Captain_Slow

Hmmm...Very expensive...less expensive....$9 spray can....and I have a tube of shoe goo

Captain_Slow

I wish I had thought to take a picture of the white paper towel I sat the MAF on while spraying the cleaner. The MAF looked clean before cleaning, but spraying just the thin wires and the circular part of the pedestal anchoring the wires produced a light gray stain on the towel. Someone at Camp 928 told me that after shutdown the wires in the MAF are heated to red hot to burn off oils and dust, but a residue can remain. I'm guessing this is what the cleaner removed.

I'm sure the MAF is near the end of it's life, but it is working well now. To follow up on Stan's advice and to have a good spare I'll look for a used one to have rebuilt (submit as a core). Roger says used MAFs are in such short supply they can't provide rebuilds without the customer cores.

ROG100

We have plenty of rebuild MAF's in stock and currently cores are not a problem.
We stock both rebuilds by Injection Labs ($325) and JDS ($375).

A MAF cleans itself - every time you turn the engine off and do not restart within two minutes the MAF goes through a cleaning cycle. All the filaments glow red hot to burn off any residue. You should not need to clean a 928 MAF as it does it itself.

NoVector

I was talking to Roger at 3rd Coast about MAFs and he said John Speake has some basic tests on his website. It's worth checking out. http://www.jdsporsche.com/faq.html

Wolfman928

hey dude, you stole my car ! cool idea on cleaning the MAF, where do I start to remove mine ?

best
J

Captain_Slow

Thanks Roger. Glad the situation has improved with the higher core charge encouraging people to return the core. It makes sense that the MAF should be able to clean itself. Perhaps one of the signs of a dying MAF is the wires no longer getting hot enough to completely clean themselves. Hopefully I've bought a little time by cleaning it.

Thanks for sharing this!

I actually paid a little too much for it at the time Remove the air inlet tubes and air cleaner (easy). The bottom section of the air cleaner sits on the top of the MAF. Notice I removed the fuel rail cover and disconnected the fuel injector connection. This is all part of my method for making it easy to remove the MAF. It's only easy if the clamp on the rubber elbow the MAF slides into is oriented so the screw head on the clamp is oriented so it faces the exposed fuel rail. I'm able to insert a long screw driver or 7mm socket with universal joint on a long extension on to the clamp hex screw. There's a nice line of sight under the rear of the intake. You can also reach around the backside and feel for the hex screw but it's hidden. Leave the electrical connection on the MAF while removing it. Lift it out slowly (be careful to not accidentally pull off the black main vacuum line that runs under and connects to the underside of the intake manifold (I learned the hard way). After you have the MAF lifted up a bit you can easily remove the connection from the drivers side using a small screw driver or pick tool to lift the retaining spring clip enough to slide the connector off the MAF.

XS29L9B

Could the "residue" have been the gunk in and around the actual "sensor" part of the MAF? In other words cleaning the housing, more than the hot wire itself?

It's good to see the MAF can be rebuilt. On another car I have, the Bosch MAF has no service replacement, and no apparent source for when it goes "bad", although the SES will show a code for MAF Failure, at lease, leaving no doubt.

Curious on your further thoughts, and glad to hear the car gained some pep.

FredR

Jon,

If you have not done so already it may be prudent to check if the burn off feature is actually working- remove the air filter and then shut the fully warmed up motor down and look down the bore. You should be able to see the wire glowing red very clearly. Not saying that cleaner stuff did no good but it should not be necessary.

Captain_Slow

Fred - Thanks for this suggestion. I didn't even think this would be possible. EDIT: I just read the JDS information about testing the MAF. Excellent information. I'll perform the voltage and ohm measurements as they will provide information about condition of other components.

FredR

The car will run fine with the air filter removed and that can be done with the motor running. Do not run it this way for any longer than needed and not during a dust storm!. You may also find it easier to see what is going on using a mirror at 45 degrees over the MAF.

Jason89s4

Thanks for the thread, I'm going to order a can. While the MAF is designed to be "self cleaning" you've discovered that cleaning it does help. If it worked, it worked!

MrMerlin may chastise me, but I'm not a big fan of replacing components like the MAF solely out of fear of future failure.....when doing restorations there have been numerous times that I've put new off-the-shelf items on cars that didn't work as well as the original. Everything on any car will fail eventually, but if that keeps you up at night, just go buy a new car.

Yes, your MAF car will run fine with just the top of the airbox and the filter removed so you can perform Fred's suggestion. (FYI and off topic, I've found that this is not true for early CIS cars. The idle will be high until you put everything back in place.)
-Jason

FredR

There is an interesting flip side to this thread.

We know that aged MAF's under read the air flow by a few per cent and this typically seems to happen around 60k miles or so and impacted by the number of burn off cycles- short trips more cycles etc etc. Our perception is that the burn off cycle not only burns off any residual crud but also a few molecules of the platinum wire as well leading to an increase of electrical resistance and thus the false reading. Now, whether or not our MAF guru's like john have been able to detect an increase in resistance by measurement I have no real idea but crud on the wire in whatever form would also alter the calibration resulting in under reading of the air flow.

This begs the obvious question as to whether the perceived cause of the aging degradation is what we understand it to be. I suspect the original perception holds correct but maybe some of the MAF's under reading do so because they are not fully burnt off- thoughts?