So, I cleaned my MAF last weekend...

Last weekend was busy. On Saturday I changed my alternator out (it burned up and I drove 40 miles on a draining battery). On Sunday golf ball size hail tried to destroy my car (it now has a few dozen decent sized dents in it), I changed my air filter, cleaned my snow screen, and cleaned my MAF sensor.

So all last week I have been enjoying a massively more responsive little diesel car. I mean, it is so surprising how much more power and zip it has. I'm talking literal surprise when I take off. Wheels spin. I get pushed into the seat. My eyebrows raise and I smile.

I used the CRC Mass Airflow Sensor spray cleaner. There was so much oil and junk on the sensor and in the housing. I sprayed and sprayed, and black kept coming out. I did that until clear came out, then let it dry before reinstalling it.

However, my fuel economy dropped a few. My fuel economy hasn't been great for a long while now, and I am trying to figure that out. I was hoping that it was the MAF, since it was so dirty. But I just filled up this evening and my MPG calculated out to 35. I usually get a pretty consistent 38.

So I figure there's two reasons. First is my foot became heavy because of the MOAR POWER factor. It's just so damn fun now. Second is that the computer didn't compensate (properly) for the newly clean MAF.

Is the second option actually an option? Wouldn't it automatically run better if the MAF was filthy and became clean?

38 mpg to 35 mpg is about a 10% drop. A heavy foot can easily cause this amount of change.

Generally, cleaning a MAF doesn't produce very good results. Because this is such a critical component it's recommended to replace it with a new BOSCH one: don't be tempted to go with a cheap MAF as you'll likely end up replacing that within a short period of time (and kicking yourself for trying to go cheap).

Guessing what's happening with these cars can lead to spending a lot of money. Finding and correcting issues quickly and spending the least amount of money possible can only really happen with the aid of a good diagnostic tools such as VCDS (it's the "community approved" tool).

The mpg change could easily be from how you are driving it. Or tire pressure, etc.

What is more worrisome is the presence of oil and dirt on the MAF.
It should be clean and whatever is getting on it is getting in your engine, too.

Oh yeah, flee is correct. Should be concerned as to why the MAF is that yucky! That should ONLY be fresh, clean air coming in to it! Um... any chance this has an aftermarket air filter (like a K&N)?

UhOh said:

Oh yeah, flee is correct. Should be concerned as to why the MAF is that yucky! That should ONLY be fresh, clean air coming in to it! Um... any chance this has an aftermarket air filter (like a K&N)?

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That is a big concern (or would be if it were mine) and shows classic signs of a K&N type over-oiled foam rock screen/filter. "Cleaning" a film type MAF isn't typically recommended, but when you have nothing to lose, why not, I guess.
I would be looking for a replacement OEM airbox if it's been replaced. If it's still there a good chance it's cracked or warped cover isn't sealing.
Computer/ECU uses real time data from the MAF and doesn't re-learn.
Auto or manual?? Horrible mileage if manual.

It's an automatic. I put the filter in about a year ago. OEM filter, not aftermarket. The one I just put in apparently is the cold weather one, with the white layer on the bottom.

My guess is the oil is from the crank case vent. I doubt it has been cleaned much in the almost 240k miles it has been driven. I said junk, but I really don't think there was actual dirt on the sensor or in the housing. I think the filter (and snow screen) were doing a good job filtering out everything.

I have to say, cleaning the MAF made a huge difference in driveability. I had become accustomed to the points in the power band where it just sort of lost power. Those points are gone now, it has full power through all the gears now when accelerating.

I'd guess it was my foot becoming heavy. I still would like to try to get my overall MPG up, though. Any ideas of what to look at next? Timing is very good, I had the belt done not long ago.

A quick suggestion: have you tried driving with the MAF unplugged?

I ask because cleaning it is kinda hit-and-miss, and has been known to kill it... it's a hot film style that is challenging to clean, unlike the hot-wire type many cleaning fluids are designed for. And... a car with a dead MAF often drives with more power than a car with a malfunctioning MAF, since the ECU defaults to a stock map.

You will trigger a CEL with the MAF unplugged... but it might be interesting to know if the car's performance changes.

If it doesn't... a new MAF might restore your fuel economy... or at least be worth a shot.

marasm said:

It's an automatic. I put the filter in about a year ago. OEM filter, not aftermarket. The one I just put in apparently is the cold weather one, with the white layer on the bottom.

My guess is the oil is from the crank case vent. I doubt it has been cleaned much in the almost 240k miles it has been driven. I said junk, but I really don't think there was actual dirt on the sensor or in the housing. I think the filter (and snow screen) were doing a good job filtering out everything.

I have to say, cleaning the MAF made a huge difference in driveability. I had become accustomed to the points in the power band where it just sort of lost power. Those points are gone now, it has full power through all the gears now when accelerating.

I'd guess it was my foot becoming heavy. I still would like to try to get my overall MPG up, though. Any ideas of what to look at next? Timing is very good, I had the belt done not long ago.

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These are hot wire MAFs and cleaning them usually kills them.

The old "Cage mod" to the MAF (disconnecting and applying dielectric grease into the connector and reconnecting) was popular (and often successful). I have found it was probably more to the connecting/disconnecting action that made better contact in the corroded connector and may have played as much a part of the improvement as the cleaning may have had. Never know for sure, but nice to get the power feel back. After driving with a bad MAF it's very noticeable when it's back to "normal".

I would highly doubt it's from the crankcase vent. That's plumbed in after the maf. I would gather your airbox leaks or someone had a cone on it before you bought it.

justynd said:

I would highly doubt it's from the crankcase vent. That's plumbed in after the maf. I would gather your airbox leaks or someone had a cone on it before you bought it.

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EXACTLY!

Stock OEM airbox and new filter and new MAF and THAT should be that! If you find oil and crap on the MAF again then you've got a problem that might require seeing a shrink: you're sleep driving in places where one ought not drive!

I have tried to drive with the MAF disconnected. It loses power, drives horribly.

I'll definitely keep my eye on the situation with the MAF getting dirty. It makes sense that it isn't the CCV, now that I think about it. It has the OEM air box, but I will take a look at it to see if it is cracked or anything. Is there a particular place that it it is known to break or crack at?

I got the car at 194k a little more than two years ago. Over that time, and with the amount of stuff I have repaired, I get the feeling that the car wasn't super well cared for. I changed the fuel filter at 197k, so that's probably due again.

I'd like to get VCDS and do some checking on how it's running as I drive it daily. Are there any VCDS guides? I know I can see if the MAF is operating, but how would I know if the ECU is using a default or stock map?

marasm said:

I have tried to drive with the MAF disconnected. It loses power, drives horribly.

I'll definitely keep my eye on the situation with the MAF getting dirty. It makes sense that it isn't the CCV, now that I think about it. It has the OEM air box, but I will take a look at it to see if it is cracked or anything. Is there a particular place that it it is known to break or crack at?

I got the car at 194k a little more than two years ago. Over that time, and with the amount of stuff I have repaired, I get the feeling that the car wasn't super well cared for. I changed the fuel filter at 197k, so that's probably due again.

I'd like to get VCDS and do some checking on how it's running as I drive it daily. Are there any VCDS guides? I know I can see if the MAF is operating, but how would I know if the ECU is using a default or stock map?

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What does "drives horribly" mean? You have to give us meaningful descriptions. On an otherwise well operating ALH if you unplug the MAF it will feel like an utter dog. The POINT about unplugging the MAF is to find out whether it alters smoking or other rough running issues. Unplugging the MAF places the ECU in "safe" mode- it no longer tries to operate based on signals from the MAF; if the MAF's signals are wonky then the ECU ignoring them OUGHT to make for a smoother running, but dog of an engine.

There's more than plenty on how to use VCDS: use search.

Forget about trying to go to the "advanced" stuff of trying to see if you're running a non-stock map. Get the data and we'll tell you whether that's the case or not: in general the tell-tale will be how much fuel is being requested. Let's first concentrate on finding out what the problems are.

How are you calculating your FE?

You state that you last changed the fuel filter at 194k miles. I see you note you have 240k miles now? This would imply that you're WAY beyond the change interval. You need to get a handle on maintenance intervals: there's a thread around that has them. I have a quick cheat sheet on each of my vehicles showing when last regular maintenance activities have been performed and when the next ones are due: I've sync'd them to match up with 10k mile intervals which means every time I see the odometer working towards and even 10k mark I know to see what maintenance is coming due (won't work for those in KM land ).

our mafs can be cleaned successfully ... i remove them from the housing to get a better shot at the hot film and spray opposite the direction of airflow ... i always test afterward by graphing requested vs actual in vcds ... lets put it this way, i've had a new maf on the shelf for over three years and i've cleaned dozens of dirty unresponsive/slow responding units in the meanwhile

marasm said:

I have tried to drive with the MAF disconnected. It loses power, drives horribly.
I'll definitely keep my eye on the situation with the MAF getting dirty. It makes sense that it isn't the CCV, now that I think about it. It has the OEM air box, but I will take a look at it to see if it is cracked or anything. Is there a particular place that it it is known to break or crack at?
I got the car at 194k a little more than two years ago. Over that time, and with the amount of stuff I have repaired, I get the feeling that the car wasn't super well cared for. I changed the fuel filter at 197k, so that's probably due again.
I'd like to get VCDS and do some checking on how it's running as I drive it daily. Are there any VCDS guides? I know I can see if the MAF is operating, but how would I know if the ECU is using a default or stock map?

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When you check the airbox there is one source that could let dirty air in before the MAF.
Make sure the vacuum vent hose is connected to the nipple under the MAF area.

I'd cleaned my MAF several times over the years. Each time it improved drivability but it was never as good as "new". I finally decided to just replace the poor thing. I took it out of the housing, and it was FILTHY. Yup. Before you ask, I did run a K&N filter for several years. They're great filters, just not for a TDI.... Been running MANN cold region filters for the last 5 years or so.

Symptoms I was experiencing: Acceleration was....awful. From 0-50% throttle at lower speeds it was ok. ish. Power surged HARD from about 2200-2700 RPM then STOPPED at 3kRPM. It was like I had a 3000 RPM limiter. Power on the highway was fine as long as roads were level. With the cruise set speed would drop quite a bit when going up hills. Holding the accel button on the cruise control did nothing unless going down a hill. No passing power. No fun. Frustrating. There was never a MAF code on vcds either.

Back to the story. Went to the trusty local VW dealer$hip and they said they could probably order one in for ~$250. I found a BOSCH MAF on Amazon for $76. Yeah. Difficult decision there. Two days later it arrived, ten minutes after that I was on the road. Aaaaannnndddd....results. were. apparent. immediately.

You couldn't jackhammer the grin off of my face. Acceleration was smooth and linear in every gear and at every RPM. You can see the mods in my sig block. They're doing their job now. The car has never had this much fuc#!ng power. It'll flat out plant you in your seat. I hooked up the vcds and adjusted IQ from 4.6 to about 5.2. That got rid of most of the smoke on full throttle acceleration and should help my MPG a little bit provided that I do my part and not drive it like I stole it. Time will tell.

Sorry for the novel but I figured it was relevant. My little oil burner is more fun to drive than ever.