MAF issue out of the blue...

[Lionheart]

Hi guys

Need some help please!!!

We have a 2004 RS6 which has a Unit 20 stage 1 remap (2-3 years back) and also a Milltek decat exhaust.

I spoke to Martin at Unit 20 before we bought it as the engine management light was on due to the decat exhaust throwing off the Lambda sensors. He advised he's have to do a custom remap from scratch as decat is usually for stage 2 remaps. He said he'd re-do the stage 1 remap, with a custom feature to disable the Lambda's (as per a stage 2). For £500.

Thankfully the previous owner included the cats! So, my thought was swap it back to the cats and Lambda sensor issue should be solved. Reset the fault with Vag Com and the engine management light should not come on again. So, that's great in theory.

However... Now on to the problem...

I took the car to a local garage who do a lot of work for us. They are not an Audi apecialist, but do have a very decent standard of work.

The job was to remove the decat downpipes and replace with the original catted downpipes. This involved dropping the subframe, removal of the suspension etc. So a 3-4 hour job.

This was done successfully!!!

However, they have noe advised that the car is idling very badly, and there is a MAF Range Performance fault showing on diagnostics.

Argh!!!

The garage said that it's probably something to do with the remap, and now the car is not getting the correct airflow for the adapted remapped settings.

They also noted that if you remove the airbox (and so also MAF sensors) then it idles PERFECTLY!!!)

So, I called Martin at Unit 20 again to confirm this...

[by the way - Martin is a star - if you own an RS6 and live within a reasonable distance (+ and hour!) then don't use anyone esle!!!]

Unit 20 advised that the MAF settings ARE NOT adjusted as part of the remap, and he immediately said that what's probably happened is that they've broken the MAF sensors if they did not remove the airbox in advance of dropping the engine, or maybe broken some the MAF wires etc.

So I called the local garage again. No, they definitely removed the air box prior to dropping the engine, and we also agreed that it's unlikely that BOTH MAF sensors would break at the same time (although possible!)

They're going to recheck everything in the morning, and check for any damaged wires as well.

So, what do you guys think may have happened here??

The car idles perfectly with the airbox and MAF's removed, and idles like crap with the MAF's in place.

What on Earth could be causing this????

Please help!

[JCviggen]

Either they didn't put the airbox back properly (not sealing) or they screwed up the fragile metal/rubber rings that seal the MAFs in the process. Either way it's an unmetered air leak issue.

Both are very easy to do if you don't regularly work on an RS6.

Bloody typical for them to blame it on the remap as well, such an easy cop out.

[Shoppinit]

What he said.

[stealthyspeeder]

The car idles perfectly with the airbox and MAF's removed, and idles like crap with the MAF's in place.

What on Earth could be causing this????

Please help!

http://forum.rs246.com/viewtopic.php?f=2&t=97855

I had similar symptoms recently, turned out to be a vacum pipe that was broken. I must have bumped or stressed it when I removed my coilpacks. I would check them all.

Does the idle get a bit better after the SAI finishes?

[Lionheart]

Many thanks for the reply!

Hopefully it will be a damaged/crushed vacuum pipe somewhere so will be quite an easy fix!!! I'll get the garage on to that now. Much appreciated!!!

Excuse my lack of knowledge here, but basically in theory the MAF reads the air 'quality' coming into the engine and adjusts the throttle setting accordingly. So, of for example, you were at higher altitude that the MAF would 'read' the thinner air coming in and adjust the throttle and so air/fuel mixture accordingly.

So, it basically controls how the car 'adapts' itself to the quality of incoming air. And so if it's not getting incorrect readings then this would indeed lead to a bad idle - as in this case?

Is my basic understanding correct?

If so, is there any reason to ever change the MAF settings when doing any kind of remap or conversions?

Just trying to get my head around it and expand my knowledge a bit!

Thanks guys!

[Nobby]

The MAF does not read the quality of air, it will read the quantity of air. More air generally equals more fuel. There are a multitude of other sensors that have inputs towards the running of the car though, throttle position, engine load, rpm, air temperature, possibly even a MAP sensor to monitor pressure.

High/low altitude is dealt with by things like atmospheric pressure sensors.

I'm a little puzzled how you can remap a car without adjusting the fueling based on the MAF readings though.

[Lionheart]

Hi Nobby

Many thanks for that!

Yes, the local garage is saying they cannot understand how the MAF setting could not be affected.

But when I spoke to Martin at Unit 20 yesterday he was resolute that the MAF settings are not adjusted for the remap (which is one of theirs).

So I'm confused now as well!!!!

Not sure what to do as Martin has said one thing, but the local garage are saying another (as is Nobby).

Argh!

[Shoppinit]

Either they didn't put the airbox back properly (not sealing) or they screwed up the fragile metal/rubber rings that seal the MAFs in the process. Either way it's an unmetered air leak issue.

This.

[Maximo]

I would more inclinded to listen to Grizz (Martin) from Unit20 than a run of the mill garage, no disrespect intended, but Grizz deals with these cars day in day out and really knows what he's talking about.
Adding to that, if he did the remap then he's going to know what he did and how it's likely to be effected. If I were in your position I'd take the car to Unit20. Where abouts are you in the country?

[Nobby]

NB: I'm not saying Grizz is wrong - i think its the MAF seats/air leak problem too

But, if anyone can tell me how you remap a car without taking into account MAF values then that'd be great. Otherwise what is the point in the MAF(s)

[Lionheart]

Good news!

I called the garage and the fault now seems to be fixed.

They are not certain why/how!

Basically, after scratching their heads yesterday and seeing the fault EVERY time the airbox was refitted, they left it out overnight and also decided to leave the battery disconnected to reset any systems.

Then this morning they carefully double checked EVERYTHING. Could not find any damaged vacuum hoses, wires etc. Put it all back together, started it up and perfect first time! So, they tried it a few times and took it on a test drive etc to see if it would start playing up again, and now it's absolutely fine.

My guess is that either there was a pinched vacuum hose or a seal somewhere that was not sealed fully yesterday, but was ook when they re-connected it all back together again.

Or, leaving the battery off has reset something and now it's happy again in its reset state.

They're going to keep an eye on it and test before I pick it up and run disganostics again etc. But seems 100% solved.

How weird!

[Shoppinit]

My guess is that either there was a pinched vacuum hose or a seal somewhere that was not sealed fully yesterday, but was ook when they re-connected it all back together again.

This. I hate taking the airbox off. Or more precisely, putting it back on. I've done it loads of times, and I'm still paranoid when I do it.

[perthwaRS6]

As another poster once said "every time you take the airbox off and refit it, your MAF seals die a little bit"

And if not refitted correctly, all the MAF not sealing problems raise their heads!

Been there, done that, bought the t-shirt and paid dearly for it.

john

[chunky79]

The only thing you have to worry about when messing about with the airbox/maf's is dropping something down the inlet! Everything else is just a little bit of wasted time.
Grizz uses some blanks to cover the inlet which is a great idea. (other specialists are avaliable)

[Nobby]

Put some rubber gloves over them - that works.