# MAF sensor? *FIXED*



## Guest (Jul 24, 2011)

This may be a bit of an obvious one but it would be good if someone could confirm...

Over the last couple of weeks my idle has been getting progressively worse (APX 225 quattro) and everytime I come to a stop my idle drops to about 650rpm and then recovers to around 850/900rpm. I have checked for fault codes several times and there is absolutely nothing. I have read that MAF sensors can cause idle problems so this afternoon I unplugged my MAF and went for a spin. The results were;

- ESP light on (I expected that)
- No more dips in idle
- Idle generally seems smoother
- I have more power!!! 

So... this may be a silly question, but does this sound like my MAF is dead? I think it does, but I didn't want to jump to conclusions as I thought disconnecting the MAF may just be masking another problem.

Another bit of info to add - the idle is completely fine when the engine is cold. As the engine warms up it gets increasingly worse.


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## james 91 (Jul 12, 2011)

Rough running when the ECU uses the MAF sensor, Smoother when it doesn't - Sounds like classic MAF failure to me


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## benfunktion (Jan 24, 2011)

mine is similar

replaced MAF - no change :-(

does yours hold back under load when the MAF IS connected by any chance?

i'm hoping someone can help me with this too so if i find out anything i'll let you know as it sounds similar


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## Hoggy (May 8, 2002)

Hi Tezray, Change the MAF & make sure you get a genuine Bosch one. 
Hoggy.


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## Guest (Jul 24, 2011)

benfunktion said:


> mine is similar
> 
> replaced MAF - no change :-(
> 
> ...


Thanks for your input guys 

Mine doesn't seem to hold back at all under load and generally it drives ok. Disconnecting the maf did increase the power quite considerably though. If I get a new maf can I expect it to drive the same as when the maf is disconnected? Does having the maf disconnected run the engine quite rich?

One question on buying a new maf, I thought I had read somewhere that GSF will take my old maf and sell me a new one at a nice price? Like £70 for a refurbed Bosch one?


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## Hoggy (May 8, 2002)

Hi Tezray, Engine will run rich with MAF disconnected, so not advisable to leave for long periods. MAF is usually an exchange item, just make sure its genuine Bosch.
Hoggy.


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## Guest (Jul 24, 2011)

Will do cheers Hoggy. I know of 2 GSF's in Bristol so hopefully one will have the maf I need in stock and I can pick it up on Saturday 

I've read several stories of cheap maf's being complete rubbish so I will be sticking to Bosch!

I'll update with the results when I have a new maf, fingers crossed it will drive/idle better and return slightly better fuel economy 8)


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## benfunktion (Jan 24, 2011)

Hoggy said:


> Hi Tezray, Engine will run rich with MAF disconnected, so not advisable to leave for long periods. MAF is usually an exchange item, just make sure its genuine Bosch.
> Hoggy.


Hmm this contradicts what i'm experiencing and what i've been told. I was lead to believe that without information from MAF the ECU goes into a kind of limp mode and opens wastegate permanently to reduce risk of damage. with no maf mine has virtually no real power to speak of at all, I hear the turbo spin up but it does nothing perfomance-wise which would kind of backup the theory.

My bosch exchange one was £60 i think

good luck, let me know what happens


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## james 91 (Jul 12, 2011)

benfunktion said:


> Hmm this contradicts what i'm experiencing and what i've been told. I was lead to believe that without information from MAF the ECU goes into a kind of limp mode and opens wastegate permanently to reduce risk of damage. with no maf mine has virtually no real power to speak of at all, I hear the turbo spin up but it does nothing perfomance-wise which would kind of backup the theory.


No mate, that's incorrect.

Without a signal from the MAF sensor the ECU calculates fuelling from a backup map using the MAP sensor. This is a lot less efficient than using the MAF sensor and thus runs less smoothly.

Your correct that in Limp mode the ECU either opens the wastegate, DV or both to limit boost to safeguard components. It seems to me that this is what your experiencing. Have you scanned for codes?


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## benfunktion (Jan 24, 2011)

james 91 said:


> benfunktion said:
> 
> 
> > Hmm this contradicts what i'm experiencing and what i've been told. I was lead to believe that without information from MAF the ECU goes into a kind of limp mode and opens wastegate permanently to reduce risk of damage. with no maf mine has virtually no real power to speak of at all, I hear the turbo spin up but it does nothing perfomance-wise which would kind of backup the theory.
> ...


james, just so's not to hijack Tez's thread, mine's here.. 
viewtopic.php?f=2&t=244825
thanks mate


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## Guest (Jul 24, 2011)

Ok well i've replaced my MAF sensor for a genuine Bosch unit and it's exactly the same 

I'm going to run a log on blocks 031 and 032 for lambda readings and go from there.

I think as the problem goes away when the MAF is unplugged it must be a fuelling issue? If I had a vacuum leak it would be present with MAF plugged or unplugged?


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## benfunktion (Jan 24, 2011)

i'll be watching this closely

i'm now lead to believe my issues are two different ones, one of which being the same as yours.

can i post videos on this forum?


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## Guest (Jul 24, 2011)

Just an update to let everyone know this is now sorted and I believe it was the MAF sensor.

Initially it didn't seem to have any affect, but gradually my idle improved and it became smoother to drive. Now it's perfect!! Maybe the ecu took a few drives to adapt to the new MAF? I had no fault codes to clear and I didn't do an ecu reset, so I think it just had to adapt to it.

Anyway, all sorted now so i'm a happy man


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## jason69 (Sep 25, 2012)

sorry to jump forum I own a Audi tt on a 2007 plate with triptronic gearbox, I have noticed over the last week when I put my foot down and get up to about70mph the car splutters for a few second etc. its ok if I drive up to 50mph, I have put redex injector cleaner in and still the same? I only travel around 70 miles a week? so not sure if its get crap in it and needs a good run out? I took it on motorway for 1 hour today and still the same? add it serviced around 2months ago there no warning lights on car etc. any advise or ideas on this matter will be appreciated 1 am worried if its gearbox problem, car done 34000 miles


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