How to Test if MAF is working correctly
 

Has anyone ever tried to test to see if their MAF Sensor is working correctly by the below method?

http://en.wikipedia.org/wiki/Mass_flow_sensor

"Manufacturers claim that a simple but extremely reliable test to ensure correct functionality is to tap the unit with the back of a screwdriver while the car is running, if this causes any changes in the output frequency then the unit should be discarded and an OEM replacement installed."

I think I might try this at home tonight and see since I've been getting the ever so common P1128/P1130 CEL code.

I haven't tried this. While I'm certainly no expert, I think it's fairly safe to assume that you'll know if your MAF isn't working correctly. When mine began to fail it was extremely noticeable.....

Link didnt work for me, I tested mine by unpluging it if it runs better its bad. If its unplugged it will go to a set parameter of a/f this is not a WOT test by the way.

Hi,

There are two types of MAF sensors. One uses a thin wire while the other uses a hot conductive film (foil or metalicized Mylar). I'd be leery about tapping either one of them. Unplug it while running, it's just as good a test and virtually non-destructive...

Happy Motoring!... Jim'99

In the mid to late 80's GM used to tell us techs to test the MAF by tapping on it. The problem was that some techs had rather heavy hands and I used to see sensors with holes or even worse damage...... that test method was soon discontinued. I wouldn't use on the newer sensors

How does a car with a bad MAF run? Idles poorly? Less power?

Does it come on gradually or will it suddenly go bad one day?

Hi,

It runs poorly. The ECU (DME in Porsche Parlance) cannot get an accurate signal indicating the Mass of air entering the Intake, therefore, it cannot select the appropriate Fuel/Timing MAP to maintain a stoichiometric mixture (14.7:1 for 92 Octane Gasoline). Then the O2 sensors give it even more confusing or non-corroborating information. Eventually, the DME will select a default MAP often referred to as Limp mode. Starting, Performance, Idle, and Range (MPG) can suffer. It can degrade progressively, or suddenly. Hope this helps...

Happy Motoring!... Jim'99

Maf
 

I'm thinking about installing an EVO cold air intake in my 02 Boxster S. Is there anything I need to be concerned with regarding the MAF?

Thanks,

I remember hearing from 2 members that after they installed the evo cold air intake, they received MAF codes and only went away after going back to stock intake... also, they were not satisfied with the power gains of the new evo intake.

MAF Testing
 

Thanks for the response OhioBoxster...

I unplugged my MAF (with engine off), started-up, and drove around town. My engine still did not perform well, having 1st gear acceleration problems, as well as small backfire popping sounds. Did you unplug your MAF while your engine was running and only let it idle or did you drive around with it unplugged? Either way, I have ordered a new air filter and new MAF sensor and will be installing both once received by next week. I have a feeling that my problems will still exist, but that will be ruled out. Any comments are appreciated.

Hi,

Without a MAF (or a malfunctioning one), unplugging it should have the exact effect you experienced. Replace the MAF and I bet you're good to go...

Happy Motoring!... Jim'99

Interesting, you described a popping sound. Have you done anything else to the car lately? When I had a popping sound it was due to a vacuum leak. Its a big long boring story but it ended up being a broken oil tube. I tought my maf was bad too and as it turns out it probably wasnt. Does your car have a rough idle? When the car is cold it takes readings from the maf until the 02's heat up. The car switches back and forth between 02's and maf. Another question, do you get a check engine light? If so another board member turned me on to running the car to Autozone and getting them to tell me the code for free. I bought a code reader on e-bay since then so I can read my own codes now.

One thing to keep in mind is that if the MAF does go bad and is not replaced in a timely enough matter you can foul your plugs. When my MAF went out I had it replaced and they cleaned the plugs. But just a few days later the problems resurfaced and they determined they had to replace a couple plugs.

Just an idea....

Hi,

Sorry, the car does not rely on MAF readings when the engine is cold. It takes only approx. 10-15 sec. for the O² Sensors to come up to operating temperature, they are heated sensors with an induction coil or heater to do this. Until then, the DME operates in what is termed an Open Loop, meaning that it isn't sampling anything, just operating on a default MAP.

The MAF Sensor and O² Sensors work in conjunction with the DME in Closed Loop operation where the Air Mass measured (along with other variables like Engine Temp, Load, Speed, Fuel Quality, etc.) determines which Fuel/Timing MAP is selected.

The Pre-Cat or Primary O² Sensors verify or corroborate this selection with post combustion Oxygen Sampling, which is further refined by the Post-Cat, or secondary, O² sensors sampling the same exhaust pulse to determine the Cats efficiency in managing the Emissions requirements.

One of the reasons (but not the only one) why an engine with a failed MAF will exhibit popping is that the DME gets an unrecognizable signal (including no signal) from the MAF. If the MAF has failed, the signal is interpreted as too much Intake Air and the DME enriches the mixture, which then does not fully combust inside the combustion chamber and passes through to the hot exhaust where it spontaneously combusts causing the Pops. On primarily a dirty MAF, the dirt/oil acts as insulation not allowing the Intake Air to extract any heat from the Hot Film. The resistance or voltage (depending upon type) doesn't change which the DME interprets as a lesser Air Mass. Consequently, it leans out the Fuel Mixture, often resulting in poor starting, low performance, hesitancy. Just FYI...

Happy Motoring!... Jim'99

Another good way to test the MAF:

1) Start car and drive around while taking notice of performance.
2) Remove MAF and smash with sledge hammer.
3) Reconnect what remains of the MAF.
4) Start car and drive around. If car runs worse with broken MAF than the MAF was probably okay prior to step number 2.

:D

I listened for a vacuum leak around my oil filler tube, cap, etc. and couldn't hear one, but that's not to say there's a leak somewhere. My idle really isn't that bad. Maybe once in every 30 times I drive it, it does a weird pulsing idle at stoplights, but 95% of the time, the idle if fine. My problem is when I accelerate in first gear, it hesitates and somtimes a popping sound is associated with it. I do in fact get a check engine light and have a computer reader and the codes are P1128 and P1130 and that is what I have been researching thus far and why I've mostly pinpointed my problem to my after market air filter assembly and MAF sensor. Any other comments are always welcome..thanks

Sounds like the caveman method...this is usually the way I handle my car problems..ha ha.

Now my Idle is erratic
 

Alright guys, here's the update:

I replaced the MAF as well as the air filter and reset the CEL. After two weeks of driving, the P1128/P1130 codes have never reappeared and the cars appears to be driving well (no more popping/back firing sounds), BUT I have a new problem:

When at idle, the rpms jump from 850 down to 400-500 rpms and then back up over and over (looping). The lights on the dash even dim/flicker when the rpms drop. The car hasn't yet died because of a low idle, but it sure does come close. I DO NOT have any CEL now, so I'm not sure where to start. I have read that it might possibly be an O2 sensor or a vacumm leak, but who knows. Any suggestions are highly appreciated. :eek:

I get that same hunting idle even with no CEL... It could be a number of things from plugs, cats, o2's, throttle body cleaning, compression that could cause this.

mentioned flickering of dome light etc. Same problem for me dont think its alt. or batt.
Have cel on with wandering idle my s has alittle over 60k Im going to replace all 4 02 sensors and my maf. If the problem persists Ill go from there.