# MAF/DV problems



## essex stu (Sep 13, 2014)

Hello again all!

I know that MAF's are prone to fail - ive had mine for at least 7 years, and for the duration, had a remap, BMC air box (Regularly cleaned and stringently oiled and wiped etc after - many electrical contact cleanings of the MAF post air filter clean in this time.

If the MAF is faulty - will it always throw an engine management light/code?

Ive changed the PCV system hoses and PRV hockey puck valve lately, (NOT the DV) i'm getting a nice hum through the air filter which i'm definitely saying is the sound of healthy breathing and definitely not turbo failure .. Anyway, with my limited knowledge, I think the MAF may be faulty because ~(my understanding is) MAF Issues =

the car can run low at idle (mine is about 600 rpm when should be 800-900 ish),

the car won't splutter when removing the MAF connector with the engine running (disconnecting makes no difference REALLY, very very slight splutter for 0.2 second when making contact between prongs and MAF, maybe very slightly higher idle RPM with MAF connected but very slight)

will keep wastegate / dump valve open, or more open, to protect turbo if air levels are not fully known (Don't get as much of a PSSSSSSSSSSSSSSSSSSSSSSSSST sound from dump valve for about 6 months..

Car Runs rich, fuel input now determined by MAP (air pressure), not MAF (air flow), sensor and ECU memory of throttle positions etc (car is seemingly drinking fuel rapidly) (although this prob isn't helped by slipping clutch which I know needs changing soon

Some days/engine cold lots of boost less as engine gets hot but still plenty, other days low boost... (joys of a 15 year old car I thought)

Apparently the MAF is known to fail at around 4 years, providing that you've not had a remap or custom air intake fitted, in which case it will fail sooner (according to a guy that's gone through 3).. ive had both..

Anyway I have these symptoms of a bad MAF, also I tested this electrically for resistance and just had open circuit readings across all prongs.. this is the only sensor I tested to not give me any reading.

are these all symptoms of a bad MAF? (these are just based on issues I've read/interpreted on here)

UPDATE: across prongs 2 and 3 I get a spike of about 1800 ohms then this goes to open circuit - apparently because of a capacitor? is this normal?

Strangely enough, all of the connecting/disconnecting of the MAF whilst the engine was running didn't throw an engine management light at first, and i thought usually with a bad MAF it will throw a ''no signal from'' or ''low voltage at x'' reading on the Engine management light when plugged in... This could be though because the engine was still warm from journey in, so will also try when engine is cold as I assume this affects the MAF by its design.

UPDATE: disconnected MAF whilst idling for about the 8th-10th time and it threw engine management light, I have an app dashcommand and a little OBD interface which said *See attached picture* Could it be that it doesn't throw a fault code first time and needs to log a few faults before throwing the light?

Anyway light is reset now and car seems to be as fine as it was before..

however despite my eager pessimism, at the end of the day I'm getting no fault codes regarding the MAF since I've had the car... (until manually taking it off today)

im sure I disconnected it a year or two ago and it made the engine splutter notably...

Any additional test advice/help appreciated, but I think im at the stage of ''change it and see if it makes a difference''..

Also, quickly, I took the DV off for a clean etc, and noted that when compressing spring (using a little allen key) it wasn't always fully shutting, it was like the downward motion of the spring shutting was eccentric and sometimes (30 percent of the time) after compressing spring with allen key and letting go, the valve would still stay open and could easily be blown through.

So my question for this is, maybe the MAF is fine, so if the DV is faulty (standard bosch plastic one atm), would you expect it to fail by the spring lowering/compressing off centre causing a lack of a seal? does this sound like DV failure? (as im sure it would explain the lack of PSSSSSSSSSSSSSSSST dump noise compared to before). I thought these springs would raise and lower very precisely ensuring that a seal is always made, mine seems to have some sidewards play to it and definitely doesn't always make a seal when manually compressing the spring - would this change under the natural vacuum/boost of the engine as opposed to me pressing it?

Many thanks for your help in advance

Stu


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## intott (Apr 7, 2015)

Your dv sounds caput. It should seal or pop back shut straight away. Not an expensive item to replace.

MAF sensor going bad won't always throw a code. They can degrade over time rather than straight failure. 
Imo if the MAF and dv have never been changed, I would fork out for new ones regardless.


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## audiTT3285 (Jun 12, 2016)

interesting read...

feel like I'm not getting the boost I should and fuel consumption has increased considerably...

standard 225 65k 2002 and as far as I know the MAF has never been replaced...

may pop out and whip it off and see what happens...


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## essex stu (Sep 13, 2014)

intott said:


> Your dv sounds caput. It should seal or pop back shut straight away. Not an expensive item to replace.
> 
> MAF sensor going bad won't always throw a code. They can degrade over time rather than straight failure.
> Imo if the MAF and dv have never been changed, I would fork out for new ones regardless.


Hey mate, I mean the MAF does throw an engine management if I take it off a few times and reconnect, and there is a slight difference when connecting and disconnecting whilst idling but very slight. Will throw engine light after taking off a few times, but when I reset it stays off. Haven't tried driving the car with it off yet I will do later, fuel is definitely going fast though. But my clutch is slipping a bit so this could well be the cause.

The dump/diverter noise has definitely changed considerably over the past few months, the dv does spring back down ok i.e. with decent force, when manually raised, but then a spring is always gonna cause it to do that, plus I don't have a comparison - im concerned that its not always shutting centrally thus creating a good seal.. any reccomendations on where to get a cheap but OE DV? or should I just fork out for a forge 007/8? The MAF i've found at euro parts, works out about £55 once I've used 25% discount code and returned my old one to them for £35.99 



audiTT3285 said:


> interesting read...
> 
> feel like I'm not getting the boost I should and fuel consumption has increased considerably...
> 
> ...


Hello mate, definitely take your MAF off and spray with electrical contact cleaner, doesn't need a lot but you'll be surprised at the dirt that comes off it if its not been done before! I usually do every 10k or so. I hear that if dirt insulates the heated wire inside the MAF, it can change how quickly air cools the wire and therefore give an incorrect air volume reading!

I've got a 180 Quattro remapped 6 speed 120k miles, changed cam aux belt and pcv system recently, rocker cover, sump changed and the oil strainer thing cleaned out (was some serious crud in there!) once I get the clutch done it will be like a new car (he says)  providing DV and MAF ok  ... waiting for horrendous k03s turbo difficulties lool but half looking forward to servicing it myself.. all coils/plugs are spotless, but I definitely feel as though i'm not getting as much boost or power as when it was mapped... but I guess a tired clutch can lose a considerable percentage of usable power....

does it sound like I'm trying to avoid a clutch change much? lool although I have found a clutch and flywheel (LuK) kit for £280 plus I can rent a garage with a lift for £100 per day... so all in all a good price, just have to hope my minerals grow enough to try it in the coming weeks lool

:roll: :roll: :roll: :roll: :roll: :roll: :roll:


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