Maf 101

For anyone that is interested, this is the Snap on part number:

TTXR25TPE TORX® PLUS

This worked for my MAF fasteners.

This is great. Thanks for the post, bam_bam_dip! I'll be checking out my MAF while I'm swapping intake manifolds.

Limp Mode

I have a 2004 jetta bone stock almost 206,000 miles on it and I am experiencing a limp mode zero codes and I don't have to pull off the road and cycle the key I am think after reading on here is it a slight over boost issue cause I did have to replace the hot side of the turbo hose to the inter cooler recently from a tear. I don't know how to fix it as all the fixes I have looked up say I would experience codes and need to cycle the key. all that happens to me is a loss of boost slight diesel of the engine and no power then it picks right back up after about three to four seconds. Only happens under heavy load and boost at almost the climax of a hill other then that the car runs great

This stream of consciousness is to document my low power situation, to hopefully help anyone in the same boat towards the solution.

For the past 6 months, I had been experiencing a gradual loss of power.
I would get boost, peaking at 17psi, then dropping to 14-15, and then at 2800-3000 RPMS, it would drop to 10-11psi, and you could feel a sudden reduction in power, but never got a fault code.

I have my IQ dialed back for less smoke, so I do tend to boost a bit less than typical.

I was in denial that it was the MAF, as the engine would still freely rev to redline, and even accelerate (albeit slowly) to over 4000 RPM. Early on, I did a VAG Log, and while MAF and Boost response seemed a bit slow (my IQ values could account for this), I was getting reasonable tracking, and IIRC, a max output of near 800. It wasn't like the logs I've seen where the MAF only goes up to 450.

I have the Scangauge II with the MAF X-Gauge, and I didn't recall the values when the car was running well. Unfortunately, I couldn't seem to find anyone who had posted X-Gauge values from a good MAF, but I did recall the reading going over 100 a few years ago, and if I flogged that car, I could just about get it there.

One oddity I noticed was that the car did not smoke. Not at all. No matter how hard I beat on it. Also, contrary to every report I've read, I could unplug the MAF, and the car would run even worse.

Was the MAF causing the lack of boost, or was the lack of boost causing the low MAF readings? I wanted to be sure before throwing a bunch of money at new MAF, N75, Actuator, etc.

So I did every maintenance item mentioned in any diagnostic thread I read. Cleaned the EGR/intake, replaced all the vacuum lines, and checked the function of the VNT with a MityVac (working perfectly). Changed the air filter, fuel filter, and ran a can of DieselKleen.... but still had reduced power.

Blocked off the EGR vacuum line, to make sure I wasn't losing exhaust pressure to the intake, but no change.

At this point, I had spent less than $100 on hoses, Filters, DieselKleen and the MityVac. All stuff that I needed/wanted anyway.

Power had been getting much worse, and now my MAF X-Gauge wouldn't read above 70. It was beginning to sink in that the problem was the MAF.

Ordered one from Metalman. What an awesome vendor. Out of state, but within the UPS one day delivery zone. It's like ordering from McMaster. Order today... arrives tomorrow. No tax.

Plugged it in, took it for a drive, and everything was good in the world again.

The moral of the story is that my MAF failure was slow, and very gradual. When I began to notice it, the VAG log was inconclusive. It could have been a number of things, but by following the Low Power diagnosis threads, I was able to identify the problem, and fix it without throwing a lot of money at items that were still working.

In hindsight, I should have done more VAG logs, but living in a city with few schedule opportunities to steal the laptop from my wife, and do high throttle runs made it inconvenient. So I just lived with the issue until it became blatantly obvious.

For anyone who ends up searching for Scangauge MAF X-Gauge Readings, these are my values.

At idle with EGR working (both good/bad MAF): 8.8
At idle with EGR vacuum line pinched (both good/bad MAF): 13 (ish)
At full throttle, above 3500 RPM with bad MAF: < 70
At full throttle, above 3500 RPM with good MAF: > 120.

Anyone have feedback on these numbers from recent logs of groups 3 & 11 at WOT?

http://forums.tdiclub.com/showthread.php?t=435243

Thanks.

Variant TDI said:

For anyone who ends up searching for Scangauge MAF X-Gauge Readings, these are my values.

At idle with EGR working (both good/bad MAF): 8.8
At idle with EGR vacuum line pinched (both good/bad MAF): 13 (ish)
At full throttle, above 3500 RPM with bad MAF: < 70
At full throttle, above 3500 RPM with good MAF: > 120.

Click to expand...

Thank you, these are helpful numbers. I'll keep an eye on my SGII. Yesterday, I did a few 5th and 4th high load runs and it never got above 90 or so. I suspect mine is somewhere in between good and bad. I'm going to spray the MAF with cleaner, clean out snowscreen, check vacuum, etc., and do a few more VCDS logs. It just seems a little laggy on building up boost, but holds it fine at WOT.

Hi,
Quick question regarding the MAF and VCDS. My 2005 BEW Golf has a smoking under acceleration issue that I'm trying to diagnose. I recently bought a VCDS cable to log the MAF actual vs specified values. According the the myturbodiesel page regarding the testing to the MAF you use Measure Group 03.

When I go to that Measure Group, mine reads the EGR values, not MAF. Which Group would the MAF be? I go through all of them and I can't seem to find the right one.

Does anyone have any tips to help me out?

Hi all. For the first time ever I logged my MAF and boost during three WOT runs (uphill) from apx 2000 RPM to apx 3500 RPM. After reading over 100 posts and how-to's, I cannot seem to create a graph to interpret the data. VCDS created a "CSV" file of the information, which opens (without prompting) as an Excel file. I have tried various methods to get a good graph, but without success. (BTW, I'm ready to stop in RT next time I roll thru PA and help them re-write their "how-to's" for those of us who actually need a how-to, but that's another topic.)

Any help appreciated!

hskrdu said:

Hi all. For the first time ever I logged my MAF and boost during three WOT runs (uphill) from apx 2000 RPM to apx 3500 RPM. After reading over 100 posts and how-to's, I cannot seem to create a graph to interpret the data. VCDS created a "CSV" file of the information, which opens (without prompting) as an Excel file. I have tried various methods to get a good graph, but without success. (BTW, I'm ready to stop in RT next time I roll thru PA and help them re-write their "how-to's" for those of us who actually need a how-to, but that's another topic.)

Any help appreciated!

Click to expand...

Steve, it can be done in excel but takes a little while to figure out if you're not a regular user of the software for that purpose. By far the easiest way to do this is jollygreengiants handy little app: http://forums.tdiclub.com/showthread.php?t=201161

hskrdu said:

Hi all. For the first time ever I logged my MAF and boost during three WOT runs (uphill) from apx 2000 RPM to apx 3500 RPM. After reading over 100 posts and how-to's, I cannot seem to create a graph to interpret the data. VCDS created a "CSV" file of the information, which opens (without prompting) as an Excel file. I have tried various methods to get a good graph, but without success. (BTW, I'm ready to stop in RT next time I roll thru PA and help them re-write their "how-to's" for those of us who actually need a how-to, but that's another topic.)

Any help appreciated!

Click to expand...

Send me the .csv file and I will send it back graphed with explanation. You have to do little manipulation of the file in Excel but not much. chrisidzerdagmail.com

SFHGolfTDI said:

Steve, it can be done in excel but takes a little while to figure out if you're not a regular user of the software for that purpose. By far the easiest way to do this is jollygreengiants handy little app: http://forums.tdiclub.com/showthread.php?t=201161

Click to expand...

Hi Shady- Thx for the help. I did try (in my previous search and failure) to use JGG's dropbox link. For me it opens a screen that says "zip files cannot be previewed," but after that nothing happens. The only items that I can click on for action are the "sign in" and dropbox.com symbols. Not sure what I'm doing wrong.

Curious Chris said:

Send me the .csv file and I will send it back graphed with explanation. You have to do little manipulation of the file in Excel but not much. chrisidzerdagmail.com

Click to expand...

Hi Chris, thanks for the help- I'm sending the file now.

hskrdu said:

Hi Shady- Thx for the help. I did try (in my previous search and failure) to use JGG's dropbox link. For me it opens a screen that says "zip files cannot be previewed," but after that nothing happens. The only items that I can click on for action are the "sign in" and dropbox.com symbols. Not sure what I'm doing wrong.

Click to expand...

There should be a "download" button right at the bottom of that text. You download it and run it (on a PC) and open your log files in that application.

SFHGolfTDI said:

There should be a "download" button right at the bottom of that text. You download it and run it (on a PC) and open your log files in that application.

Click to expand...

When I scroll over the download button, my cursor remains an arrow (clicking doesn't start a download). It sounds like the problem is on my end, so I'll see if I can figure it out.

Chris very nicely turned my file into a graph (thanks again!), but I didn't record throttle position, so I'll do some more runs. The raw numbers do show the MAF actual going over 900, when requested is at 850, but not consistently, and not at 3000 RPM (at 2700, 2900, and 3200). I'll just do more logs.

I was able to download the graphing app created by jollyGreenGiant (thx!) and using my high speed computer skills, figured out how to graph a new log I made. This time I also recorded throttle position, to show the WOT runs. My graph looks cool, but I'm not sure what it reveals...

But for the first time in a year, the server accepted an upload to my photos!



I think this one shows throttle:

Hey Gang,

I was trying to troubleshoot my MAF as listed in the beginning of this thread, but I don't think it quite fits the traditional symptoms.

I'm having the weak, stumbling, and smoky cold starts, loss of power and occasional bog, etc., but whenever the RPMs get above 2100, everything smooths out and the cars really gets legs. When I unplug the MAF, the car feels gutless and I don't ever hear the turbo, but it runs really, really smooth without any smoke or stumbling, etc.

TL; DR: w/ MAF unplugged, *overall* power is lower, but engine smoothness and smokiness dramatically improved.

Does this indeed suggest MAF is bad? Thanks.

VWjimmy said:

Hey Gang,

I was trying to troubleshoot my MAF as listed in the beginning of this thread, but I don't think it quite fits the traditional symptoms.

I'm having the weak, stumbling, and smoky cold starts, loss of power and occasional bog, etc., but whenever the RPMs get above 2100, everything smooths out and the cars really gets legs. When I unplug the MAF, the car feels gutless and I don't ever hear the turbo, but it runs really, really smooth without any smoke or stumbling, etc.

TL; DR: w/ MAF unplugged, *overall* power is lower, but engine smoothness and smokiness dramatically improved.

Does this indeed suggest MAF is bad? Thanks.

Click to expand...

Are you sure you read this thread?

If unplugging the MAF results in a smoother running car (will ALWAYS have less power) that means that you have a bad MAF. By unplugging you force the ECU to utilize a default map set; the commands are known and steady. With the MAF plugged in then the ECU is operating based on the signals it sees from the MAF- if the MAF is wonky then the ECU will be getting trash values, thus, garbage in, garbage out!

I had a MAF failure that was very sudden and violent. Wife's car started up and started jerking around, almost like it's DMF was coming apart. With the car running and bucking I unplugged the MAF and it went back to running as smooth as silk. BAD MAF! (swapped in a spare I had and was back to normal)

UhOh said:

Are you sure you read this thread?

Click to expand...

Nope, I just read the troubleshooting guide on the first page for the symptoms...guess I should've delved further.

Thanks! I figured that my MAF was bad, but I just wanted to make sure that I'd correctly thought through what an MAF-less would drive like.

Since I have you on the line (so to speak), UhOh, is there consensus opinion on where to buy a new MAF?

VWjimmy said:

Since I have you on the line (so to speak), UhOh, is there consensus opinion on where to buy a new MAF?

Click to expand...

I was wondering, too -- not that I need one right now, but I haven't purchased one in a long time. I paid $129 one time and $119 one time.

Bora Parts, now called Cascade German, has them for $99 plus shipping, for about $113. That's for a new, genuine Bosch part -- not refurbished and not Prothe junk.
https://www.cascadegerman.com/product/038906461c/

I get mine from MetalMan (supporting vendor): I think it's sub $100 w/shipping.

It is important to log the MAF specified, MAF Actual, MAP Actual, MAP Specified and throttle position on a full throttle run from 2000 rpm to 4200 rpm try to get 10 seconds. Then open the CSV file in Excel and filter for 100% throttle. Graph the data. The MAF Specified should be 850 (IIRC)solid, the MAF Actual will spike over the Specified as the turbo is not as linear. The MAP specified is also a solid line at 1950 or close. On my failed MAF the MAF Actual slowly dropped from 850 to 500 on the run and this failure is not a CEL activator.

UhOh said:

I get mine from MetalMan (supporting vendor): I think it's sub $100 w/shipping.

Click to expand...

And here it is, with free shipping.
http://www.metalmanparts.com/product.sc?productId=160&categoryId=38

Thanks all for an interesting and long-lived thread- over 10 years! Hopefully there's still an audience.
I have a thread that's been going for several months trying to solve a very mysterious problem with my 2005 Passat B5 TDI Wagon that's had a manual swap but hasn't run properly since it's been completed. There are no VCDS codes on autoscan and the only interesting and unusual findings concern the MAF, which is why I'm posting it on this thread.

Basically, the car idles very poorly (at 500 rpm) and there is NO throttle response when I first start it and the engine is cold. The specified MAF (SM) is steady at 850 and the actual MAF (AM) fluctuates around 400-450. As the car slowly warms up the idle rpm slowly increases but there is still NO throttle response. In about 10 minutes, when the temp is somewhere around 52-56C, the SM drops from 850 to around 450. At this point the SM and AM are approximately the same, the car idles smoothly at 860 rpm, and the throttle is fully responsive all the way to redline. If I turn the car off and restart it, it runs normally with a functioning throttle. If I disconnect the MAF there is no difference.

I've seen several threads on AM higher than SM but not vice versa. My questions are:
What may cause the situation where SM is higher than AM?
Is an SM of 850 some kind of default setting? And if so how is it related to engine temp?
Any suggestions for how to diagnose the issue?

There are many more details regarding this particular issue on my thread:
http://forums.tdiclub.com/showthread.php?t=470498

Some of the earlier issues were complicated by a malfunctioning ECU which has since been replaced and seems to be working properly. I don't know if this is actually a MAF issue but the correlation between The SM, engine temp, and throttle response is compelling and in the absence of any VCDS codes it is the only thing that may be a clue to the actual problem. Any ideas?

I don't know much about PD's, but..... that doesn't stop me from guessing.

Specified MAF is what the computer wants to see. 850 used to be the max, so it's asking for maximum flow and not getting it upon a cold start.

On the earlier engines, the timing would change based on fuel temp. Does that happen in a PD? if so, perhaps checking the fuel temp sensor when cold/hot to see if it's giving reasonable temperatures.

In this situation, I would study what changes with temperature, what temps your' getting (coolant, oil, fuel, air, whatever is measured) and go from there.

Sorry someone with real info didn't respond, but if nothing else, I'm bumping this to the top.

UhOh said:

Are you sure you read this thread?

Click to expand...

If the opening post had been written better there would be less confusion. With the bad MAF my car had more power (aka performance) but it bucked. With the MAF unplugged it had less power but was smooth.

Using the word 'performance' the way the author does is just bad writing.

I posted earlier with a bad MAF, bought a new one, and replaced the old one.

With the new MAF, the engine is overall smoother and more powerful than before with the old MAF. That said, I'm still getting MAF codes, the engine is still somewhat jerky and prone to throwing tons of smoke and be gutless when I'm in higher gears--conditions that don't change whether MAF is plugged in or not. (For instance, when driving above 40 MPH, if I want to accelerate and push the accelerator halfway down, the car belches smoke--like, people change lanes and drive by and give me the finger, etc.)

Since the new MAF is better but still problematic, does this suggest a vacuum problem? Or could bad injectors be an issue? Or...?

Thanks, y'all.

I'd take a look at the troubleshooting low-power thread. Guess is that you have a boost leak. If the car is relatively new/unfamiliar to you I'd suggest checking for intake clogging.

jimmy, check all boost hose connections for oily residue, indicating a possible leak.

UhOh and JB05:

Already did the intake cleaning. It was horrible, but all good now. I'm never even hearing the turbo spin up--no noise at all, whereas I used to get strong boost before the intake cleaning.

Could a vacuum issue affect boost? I'll check on the boost connections for oil too.

Great thread!! Learned much!
Being new here I have a couple of questions. I am dealing with a '06 Jetta.
1) Does MAF sensor have anything to do with EGR valve?
2) what is a VAG-COM? Does it read engines codes on a TDI? If so how much do they cost and where can I get one? Are they worth having one?
3) Does chipping have any effect on the MAF sensor?
I am having no power until 2000 RPM and the boost does kick you back into the seat with heavy black smoke through 3rd gear. Would MAF sensor have anything to do with this.
Thanks for your time,
Sockets