MAF problem.

[UrS6]

My car has a strange running issue where it seems really fast, then falls on it's face, then fast again, etc. I have no codes currently and the following may not be related but I think it probably is.

When logging my MAF sensors I noticed that MAF 1 registers about half of MAF 2. For instance, at idle MAF 1 is around 2.5 g/s and MAF 2 is around 5.0 g/s. As I rev the car it is about the same 1:2 ratio. When MAF 1 is at 9 g/s MAF 2 is about 18 g/s. These numbers are approximate. I swapped MAFs and cleaned both of them while out with MAF cleaner. When I logged again I was getting the same readings on the same channels. So I can rule out the MAF sensors themselves. I smoke tested the car a few weeks ago and only noticed some smoke near the intercoolers so I replaced them with SRM units. I also installed Apikol MAF seals and replaced all of the small hoses on top of the motor.

I would imagine at this point I am looking at either a MAF sensor wire issue or an air leak somewhere. One of my MAF sensor connectors is broken where the wires feed through it but the wires look ok and there is no apparent damage. I have not tested continuity to the DME yet. One other bit of info that struck me as a clue (i'm just not sure what it means) is that when I rev the motor and then take my foot off of the throttle one MAF sensor--#2-- drops back to the 5 g/s in a linear and normal way where as the other drops to 0.0 before creeping back up to it's questionable reading.

Any thoughts here? And which side is #1?

[nubcake]

Swap MAFs side to side. If the issue persists - it's time to replace the MAF.
#1 is passenger side.

[UrS6]

Swap MAFs side to side. If the issue persists - it's time to replace the MAF.
#1 is passenger side.

already did that

[nubcake]

already did that

Your initial message is a bit unclear on the subject. Did the "MAF difference" stay the same side-to-side or did it switch from one side to the other? If it's the former - MAFs are (most likely) fine, move on to turbos&plumbing. Are you running OEM software or some kind of a chip?

By the symptoms you describe - it looks like you're getting some overboost throttle cut. Which suggests that maybe one of the wastegate control lines got ruptured (likely the side that shows more air). This would throw a code unless the bin is modded.
Other possibility is bypass valve letting air through under boost (either failed itself or lines to it can't hold boost), this usually does NOT throw a code.

The list of course is not complete.

[Dmb408]

suction jet pump

[UrS6]

suction jet pump
it looks like it's in a hard to reach area. Wouldn't there be a code? And do you think it would throw off the MAF reading that much?

[Dmb408]

i cant remember what codes i got when i had suction jet pump failing, and revving RPM's (on my first RS6), but they were background codes, and think they were just the intermittent cylinder fire codes. you have to take the intake manifold off to do the SJP. It just seems like everyone's are failing these days (age brittleness of plastic most likely for that heated and cooled part).