How can you tell if your MAF is failing?

My wifes NB seems to have a flat spot above 3000 rpm. I suspect the MAF.

How can I tell if the MAF is going bad, short of getting a VAG COM?

thks, Steve

Sounds likely. Have you checked the VAG COM list for someone in your area?

You can unplug the MAF and see if the car runs better, but do note that this will turn on your check engine light. Light will probably go out after MAF is plugged back in.

The check engine light will stay on when you plug it back in, but will go off after a few days.

Flat spot in power is usually a symptom of a plugged intake. Power drops off around 2800 and power returns around 3,200 this is a plugged intake.

A dying MAF causes power to drop off around 2800 but the power never returns...

DB

N75 valve

Could be a N75 valve also. You can run oputput test with VAG-COM & check condition of valve.

Drivbiwire said:

Flat spot in power is usually a symptom of a plugged intake. Power drops off around 2800 and power returns around 3,200 this is a plugged intake.

A dying MAF causes power to drop off around 2800 but the power never returns...

DB

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In my experience (and I have a lot with MAFs), it is very hard to say exactly how the MAF will fail. Some are intermittent, some die suddenly, others gradually fade so that you don't realize the MAF was bad until you swap it.

Best diagnosis: VAGcom. Compare specified MAF to actual MAF readings. If you graph them, they should track very similarly.
Quickest diagnosis (if you have a new or known good one): swap it out and see if it helps.

You can also try unplugging it. If it's totally dead, it will help, but if it's intermitted or dying, it may not prove anything.

Dealers are fond of pointing to clogged intakes for everything but unless the intake is absolutely plugged up, it will not have as much of an effect on power as a bad MAF.

There are at least two spare parts I carry in each of my TDIs. One is a new MAF, the other is a new relay 109. If I don't need them, I know that I will come across someone who will

So does this graph qualify for being out of spec? My fuel economy hasn't been great (40 mpgUS with 75% highway driving) as an additional piece of info.



I also logged specified vs. actual boost, and had a similar question about that, which I posted in this thread. Thanks.

That graph doesn't look right. If it's possible you reversed the two, then yes, that looks bad.

40mpg is not "bad". I've said this before and I will say it again. TDI drivers with heavy feet will NOT get the ultrahigh mpg that others who stay out of the boost are reporting. I'm averaging in the high 30s in my wagon but that's with very aggressive driving and some stop and go traffic.

Thanks for the response. I followed the instructions on the Ross-Tech site, and the posted graph is for ch. 3, with column headings of "MAF (specified)" and "MAF (actual)" in the log file.

The first two points should possibly be discarded, since I started logging before flooring it.

You're right -- 40 mpg isn't bad. But it's worse than it was a couple months ago when I bought the car. I'd gotten more like 44 mpg in similar driving.

Bad maf can affect mileage.

my turbo cuts out a high speeds--would this be the maf affecting it?

cberth said:

my turbo cuts out a high speeds--would this be the maf affecting it?

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N75 or sticking actuator is more likely, also check for vacuum leaks on the lines.

I have a check engine light, sluggish performance with a DTC code reading "P0101" which translates to MAF perfromance circuit malfunction.

No rough idle just feels like its sluggish, I can hear turbo spooling. EGR and intake cleaned in December 05.

Cleaned the MAF and changed it twice. No change, still getting light and code. Checked it out on Vag-Com adaptation block 3. Specified and actual readings are way off. I can adjust the specified (currently 370) but but the actual stays stationary at 525 and will not change regardless of rpm increase/decrease.

You thoughts? Could it be I have had two bad MAFs? What else is there to trouble-shoot in that circuit? What is the N75 valve?

Any help would be great.

2000 Beetle 1.9 TDI.

frugality said:

The check engine light will stay on when you plug it back in, but will go off after a few days.

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i unplugged my MAF and now i know i need to buy a new one but my check engine light didnt go on at all. is that bad?