Maf 101

sinfony78 said:

I searched this thread for k&n filters to no avail. Can someone tell me if it's ok to use one without doing damage to the MAF?

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Dirty or oil air flowing across a MAF sensor will gradually degrade it. Oil can be cleaned off, dirt and dust will cause scratches and gouges and irreparable damage.

K&N air filters, and most other so-called cold-air intake systems, allow more dirt to pass through to the engine. Oiled filters also cause contamination of the MAF.

While all filters are important, the air filter is probably the most important. TDIs and most other turbocharged engines can such plenty of air through the stock air filter. The K&N filter does not improve performance by any measurable amount over the stock filter.

thanks for the info...is there a recommended brand filter to use?

sinfony78 said:

thanks for the info...is there a recommended brand filter to use?

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Yes, the MANN air filter with foam prefilter, available here>>>
http://www.worldimpex.com/parts/mann-air-filter-with-foam-layer_275246.html

It has a paper filter, with more folds than other brands so more filter area. And it has a foam prefilter, which means the filter will hold its integrity even if it gets slightly damp. Previous TDI models used a separate snow filter upstream from the air filter -- the MANN air filter with foam prefilter does both functions. It does an excellent job protecting the engine, MAF sensor, and turbo from dust and dirt; and it allows adequate airflow for all except very highly modified TDI engines. After you've upgraded the nozzles, turbo, intercooler, exhaust, and are ready for the hottest tune available from RocketChip or Aligator, then ask again about intake upgrades.

I've been suspecting my MAF for a while, but the symptoms were never strong enough to make me overly concerned. I haven't had it hooked up to a VAG-Com yet, as I didn't think until today that it was gone enough to be too worried about. On a short errand close to home, the MIL came on. Now I'll need to locate someone with a VAG-Com in my area.

Symptoms I've noticed, prior to the MIL. (Nothing noticeable since the MIL came on):

- when the A/C is on, I can't just slowly let out the clutch if I'm in say a parking lot, I need to slightly press the accelerator too, or else the engine stalls.
- I suspect the fuel economy is very slightly worse than it should be.
- Puff of blue smoke on cold start, but no big cloud or anything.

Likely a MAF or something else? I can't seem to see any indications on here that a bad MAF will set off the MIL.

weebl, have you run your Golf w/ the MAF disconnected (to compare)?

You want to have your static IP timing checked (in basic settings mode) in VAG-COM/VCDS as well.
Larry

l_c said:

weebl, have you run your Golf w/ the MAF disconnected (to compare)?

You want to have your static IP timing checked (in basic settings mode) in VAG-COM/VCDS as well.
Larry

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Haven't done that yet, the rain was just awful all afternoon and evening, and I got drenched enough loading up the Golf with the kids to go buy dielectric grease to try the Cage mod. (My wife took the van to go out with friends).

But something interesting did happen. We stopped to get diesel at a station about a block or two from the store. Searched the store for dielectric grease, only to learn all their electronic payment systems were down (credit or debit) and I never carry cash any more. So I decide to head to Wally World just in case they also have it. Guess what, this time around, no MIL. And it never came on the rest of the evening, despite us driving a fair bit. Possibly the light was fuel related? The tank was about 1/8 before fuelling up, and we fuelled up to a little over half a tank. Same fuel brand as last time, different station.

Will still do the cage mod and MAF disconnect in the middle of doing it once it's nicer out.

This MIL is a total unknown.
I dunno which ones actually can deassert on their own.
Do you have good fuel and air filters, and the snow screen is clear?
Larry

Fuel and air filters should be okay, but are due for changing, which I was planning on doing the next week or so. And I know I need to clean out my snow screen. But I don't think the condition of any of these are bad enough to cause a MIL.

Not sure if this theory of mine makes sense, but as I was near the bottom of my tank, could there have been some crud at the bottom messing up the EGR or 02 sensors, and with a top up, diluted it to a point where it wasn't an issue for those? Would the ECU store the codes, despite the MIL going off?

weebl, from what I've seen of the fuel sending unit, I don't think that anything weird is going to happen there when you're down to the last quantity of fuel ... unless it's so far down that your IP sucks air.

There's a check valve built into the fuel sending unit, that used to have problems on older models. It's a good idea to take that unit out though, to inspect it and make sure that it doesn't have any gunk in it.

I had replaced mine (2002 model), just because they had rev'ed the letter on it, to prevent those check valve issues ... but my original unit was totally clean. It's pretty easy to service this, mine (on the wagon) was underneath the rear seat.

I have no idea about the MIL you mentioned ... one thing that might be good to do (which shouldn't cost money) is to have your ECM scanned at one of those tuneup shops, just to find out whether there are any fault codes stored (even if there's no indicator light on).

You know the glow plugs are active in what they call After Glow (while the engine is running), I wonder if those are somehow not doing their job, whether it would affect the quality of combustion?

Clogged intake manifold (not a pleasant topic) is something to wonder about ... do you ever run biodiesel or a blend? Bio does tend to clean the crud out of the intake. Or instead, how about doing the Diesel Purge exercise? (A Lubro Moly product ... you have to temporarily disconnect your fuel hoses at the filter, when you do this, and reroute them into the Diesel Purge can, so it'll recirculate the used liquid back into the pump ... I've done it, it's not painful) Larry.

Okay, so I'm much further ahead with this problem now, and very close to getting it resolved.

Last Friday, I picked up the dielectric grease to try out the cage mod. Unplugged the MAF to test on the way to the store. There was a HUGE drop in power unplugged, the car felt completely gutless without a plugged in MAF. Tried the dielectric grease anyway after cleaning off the contacts, not expecting any change, and sure enough, there wasn't a change.

Exhausting the cheapest of the troubleshooting option, the next was my $25 VAG-Com scan, which I got done yesterday. Prior to going to the indy shop, I looked up the procedures and parts for other likely MIL causes, so that I at least know what I can get the parts online for versus what the shop could sell them to me for on the spot. In doing so, I ruled out the O2 sensors, as the ALHs don't have them, ruled out the glow plugs, as the MIL comes and goes. That still left the EGR valve, which would be warranty on this vehicle as it's just in its infancy (only 110,000 km and a 2003), or the chance that the MAF is gone just enough to trigger the MIL, but not too far gone that it is still better than no MAF.

And the results... Bad MAF and an unexpected item, which the guy says was unlikely to trigger the MIL - coolant temperature sensor reading too high.

Parts are now on order, a MAF for $93 and the coolant temperature sensor for $14. Once they are in, I'll swap out the bad parts, as well as do my scheduled air filter change (no sense in messing up a brand new MAF).

Did you just get a MAF cel? That was caused by you unplugging the MAF. The code doesn't go away by itself. Did it come back on after clearing it?

No, the CEL came on while driving one day, by itself. I did the MAF unplug just a few days ago briefly. The CEL has been coming on and going off by itself, no one has been clearing it. Stored code in the ECU says the MAF problem is intermittent. CEL hasn't come on since the scan last night, but I know he did not clear any codes, just read them.

MAF code doesn't go away without clearing. You unplugging it could (should) have caused it. The CEL and the MAF code may be unrelated. If he didn't clear the MAF code, it's still there.

rdkern said:

MAF code doesn't go away without clearing. You unplugging it could (should) have caused it. The CEL and the MAF code may be unrelated. If he didn't clear the MAF code, it's still there.

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Okay, I think I follow now. I may not actually need that new MAF, since the code on there is most likely caused by when I ran it unplugged. Crap, guess I either have a spare now, or maybe I can find a buyer locally for one.

If I'm following you correctly, then the CEL was caused solely by the engine coolant temp sensor, right?

I think when the parts come in, I will replace only the temp sensor, and see if that resolves the CEL. If so, we are planning on driving to Vancouver anyway, and part of the trip is to take advantage of our friend's staff discount at one of the very few and rare reputable dealerships for a timing belt change. I could always ask them to clear the codes. And, I could bring along the spare MAF, just in case. Maybe if all is good, they may be able to give me a credit towards my timing belt work in exchange for the part. Provided of course that Bosch is the OE supplier of these, unless the VW versions are boxed differently.

TornadoRed.....just reading and noticing. You live in San Diego. I live in MA. Cold weather up here, unlike San Diego. Question: While reading WorldImpex.com info on MANN airfilter, it says it's NOT a Cold Climate Air Filter. Would you, or any Veteran member reccomend this filter for my 01 VW NB TDI? Or is there a different filter that would be better for my car in my area....particularly for cold weather? (Not sure why it isn't good for cold climate....maybe someone could briefly explain the differences, pls)

This is what I found (below) at worldimpex.com regarding air filters

IMPEX SKU # 562797
Air Filter
NOT FOR COLD CLIMATE
Manufacturer: MANN
Price: $12.00
Availability: In Stock

More info...function checkQuantity_562797() { return true; }

IMPEX SKU # 177156
Air Filter
NOT FOR COLD CLIMATE
Manufacturer: GENUINE PART
Price: $14.25
Availability: In Stock

More info...

HoneyBeetle said:

TornadoRed.....just reading and noticing. You live in San Diego. I live in MA. Cold weather up here, unlike San Diego. Question: While reading WorldImpex.com info on MANN airfilter, it says it's NOT a Cold Climate Air Filter.

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The one you looked at is not the Cold Weather air filter, this one is >>>
http://www.worldimpex.com/parts/mann-air-filter-with-foam-layer_275246.html

maf twist on a 2000 Golf TDI????? any wisdom??

Hi everyone,

Thanks to the community for the staggering amount of information. I recently purchased my 01 TDI sight-unseen off Ebay, and after reading through a lot of the FAQ's, 101's and other assorted posts (and getting the VCDS-Lite software and cable) have been diagnosing some of the issues I noticed since bringing the car back. Cannot thank the veterans here enough for the excellent learning tools their posts have provided.

Question time now regarding my MAF. Check engine sensor came on, VAG-COM indicated the 16486 - Mass Air Flow Sensor (G70) Signal too low P0102 error. Checking things out revealed that the connection was not seated properly, and I reset it and ran more tests. Here is what I am slightly confused about. Most of the posts say that MAF-Actual and MAF-Specified readings should be generally fairly close. My tests have the Actual readings higher when hard accelerating (unfortunately, no hills in mid-Michigan where I live so I have to hop on and off the expressway), sometimes much higher. The car seems to be accelerating much better now that the MAF is actually plugged in, but I was not clear if these differences indicate a dying MAF, or if that applies only when the Specified readings are higher than the Actual.

beatin a horse... code p0237. unplugged maf, no change. tried a used maf from local salvage yard, no change. (06 tdi jetta. dgs.) warm up, idle, floor in neutral, bounce off rev limit at 4k rpm. local guy has vagcom but states "im not familier with the engine controls on a diesel". i kinda know him/trust him. he just did timimg belt on car. he does lots of import auto repairs, vw,audi,mb... but out in the country so to speak. he said he can take a look but i dont wanna owe $$ and be told "i dunno"is the rpm test and the unplug test proving its maf or are there other maybes? possible used maf is bad also..., does cel need to be reset for effects to take place?

Do you have a VCDS available? The best check is to graph MAF specified vs MAF actual. If they don't track well together, then probably you need a new MAF.

What are the other symptoms you are seeing?

Hello guys. I have an Audi A4 B5 1.9TDI 115PS from May 2000, it should be the face-lift. I bought it one and a half year ago with stated 187000 km, now has 217000.
From time to time I had bad acceleration problems. Two times it was from a thin hose that broke. This time I couldn't find any of them, but I found a small tear on a thicker one, here some pictures:




I changed it, but still the car accelerates slow. So I did the tests found on this forum:

1. With a warm engine, sitting in your driveway, put the fuel request pedal ("gas pedal") to the floor and see if the engine gets to 5100 rpms. It should get quite close, but if it stops at 4800 or less, the MAF is most likely bad.
--> it goes exactly until 4800 and stays there

2. Get a VagCom, and do a MAF run while logging MAF requested and MAF actual. Find a safe stretch of straight road, and run it from 2-4000 rpms with the pedal to the floor, shift, do it again in third, and if you have space and a reasonably legal environment, do it in fourth. In each of these runs, requested should be at 850, and you should see spikes of about 1000 in the actual. If actual <850, bad MAF. This is the best test, but other things could cause issues such as clogged intake or something wrong with the boost system throwing you into "limp" mode.
--> it was pretty hard to make a recording, because communication broke fast after 2500 rpm, but I managed to watch the values and make a small recording

link
--> green=requested, yellow=actual, red=rpm

3. I also hear an interesting noise after doing some heavy accelerating, like water running, like a small waterfall, or like little rocks running.

4. I also have a fault code

VAG-COM Version: Release 409.1-S
Control Module Part Number: 038 906 019 BR
Component and/or Version: 1,9l R4 EDC 0000SG 1064

Software Coding: 00002
Work Shop Code: WSC 06335

1 Fault Found:
17964 - Charge Pressure Control: Negative Deviation
P1556 - 35-10 - - - Intermittent

What do you guys think?
Thanks!

Great thread!

1 Fault Found:
17964 - Charge Pressure Control: Negative Deviation
P1556 - 35-10 - - - Intermittent

What do you guys think?
Thanks!

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I'd say you've got a boost leak. Look at the rest of those large hoses. The part's you can't see, look to see if there's any oily spray around.

I don't think you fixed them all. Or you didn't clear the code.

You can see pretty much oily spray in my picture, I'm guessing it came from the hose I changed. I looked as much I could also with a flashlight for other hoses.

Made a quick visit to the service today, the people were nice, swapped the MAF with another one they had there, but it didn't change anything, at least they didn't charge me with any money. Made an appointment for next week.

Should I clear the fault code? I know last time I had these problems, after changing the bad hose, the code cleared itself, and the car drove great from the first pedal after key.

I believe clearing the code will take the code away - but probably won't have an impact on the ability to drive it. Try it, and see when it comes back. if you can hook up the VCDS, so some logs of MAP/MAF requested/actual. If you have a boost leak, it'll cut the pressure when the leak starts. Our cars in NA seem to want to split where you can't see them, so using fingers to squeeze the hose where the eyes can't go will often find the problem. At least it'll find the oil spray. Good luck.

I am a newbie here. I have read through this thread and see if I can find anyone doing a MAF sensor delete. So far from what I read, it is only done by people who race.

Anyone have any info on this?

What is the point? Without the MAF, the stock tuning would cut fueling. With "adjusted" tuning, what would you have the "actual" reading be?

It's there for a purpose. Without it, you lose the redundancy of the MAF/MAP tests to tell the ECU that something's wrong. A good tune will make the machine go better, but I've never heard of one here that deletes the MAF.

EGR - that's another issue. Lots of data on that.

I'm pretty sure this is the right spot to post this but if not feel free to move it. I suspect a bad MAF sensor in my 2004 Jetta TDI BEW. I ran the VCDS MAF sensor test detailed in this thread with MAF actual and engine speed (I didn't see a category for MAF specified and the MAF group was 10 not 3?). If I'm understanding the info in this thread correctly then my MAF sensor is indeed bad but I want a quick sanity check before I go and spend $180 on a new sensor. Is my MAF sensor bad? Thanks!

I know this is an ancient thread, but a really informative one, thanks to all.

Pulled out the MAF housing and all to clean. Want to confirm that I need a T-20 tamper-proof bit to get at the membrane, please. 2005 Golf PD BEW, thanks.

Actually no, it is a 5 lobe torx plus TS fastener… what a PITA...