Depressed. Changed MAFs and car runs like sh@t

[Shoppinit]

Can't believe how gutting it is when you put it back together start it up and it runs like a tractor. Missing, hunting, chugging.

Took it for a drive so that the ECU could learn the new lambda values. Something must be wrong. It's runs badly, and it's throwing codes.

Code: Select all

4 Faults Found:

17535 - Fuel Trim; Bank 1 (Mult): System too Rich 
        P1127 - 002 - Lower Limit Exceeded - Intermittent
17544 - Fuel Trim: Bank 1 (Add): System too Lean 
        P1136 - 001 - Upper Limit Exceeded
17546 - Fuel Trim: Bank 2 (Add): System too Lean 
        P1138 - 001 - Upper Limit Exceeded
17416 - Mass Air Flow Sensor 1/2: Implausible Signal 
        P1008 - 008 - Implausible Signal - Intermittent

I'm completely demoralised.

[woodlum]

Sorry to here this or able to help you out!
Hope it's fixed soon, I absoluty hate it as well when a car of mines isn't 100%
surely there will be someone on here able to help you fix it as there's a wealth of knowledge on here.

[slimmyreed]

I had mine run like a bag of crap when I refitted my mafs after I changed my coolant temp sensor. Couldn't suss it out. Checked all the connections, removed and refitted countless times etc. Gave up in the end and disconnected them. I drove it to MRC with them disconnected, hooked them back up to show doug and it was fine.

I still dunno what caused it, or why it started working after driving with them disconnected for a few miles, but might be worth trying if you are at a loss... ( take it easy tho as you can easily fry the cats with them disconnected)

[Shoppinit]

Yeah. It takes a while for the ECU to work out the partial and additive lambda corrections. After the initial rough running, the engine calmed down after a couple of miles, but remained hesitant. And the lambda values are bad. The old MAFs are going back on tomorrow.

Maybe I didn't put them back in properly. I can't work out where the Implausible Signal is coming from.

[skyegtb]

Yeah. It takes a while for the ECU to work out the partial and additive lambda corrections. After the initial rough running, the engine calmed down after a couple of miles, but remained hesitant. And the lambda values are bad. The old MAFs are going back on tomorrow.

Maybe I didn't put them back in properly. I can't work out where the Implausible Signal is coming from.

I would start by checking the connections for both MAF's, the passenger side one especially as it is difficult to remove and could easily have suffered some damage...

[Shoppinit]

Just found this information about DTC 17416:

In response to fault "P1008" the two air mass meters are not checked for mutual plausibility by the engine control unit as might be expected. Instead, the two air mass meter signals are summated and then compared to a map value in the engine control unit. Fault "P1008" is detected if the sum total of the two air mass meters is outside a tolerance range.

Looking at the logs I made yesterday, one of the MAFs is reading about 1g at idle wheras minimum is 1.5.

If they were leaking though, why would the mixture be too rich during running?

[Blue_Thunder]

Not sure how relevant this may be, but back in October I bought a brand new B5 RS4 MAF from Audi. Fitted it and the car ran like sh1te. Anyhoo, long story short... the brand new MAF was faulty and Audi replaced it under warranty.

Long story: Unfortunately for them to honour their warranty you need to have the faulty part(s) fitted (I had swapped it out with my old MAF because the new one ran so badly), allow them to run diagnostics on it (one hour for my car, may be longer for the RS6) and if they had found that the MAF wasn't at fault I would have been liable for the one hour labour. It was a bit of a risk for me considering an hour's labour at my local Audi garage was around the price of the MAF. Thankfully it was at fault!!

[Shoppinit]

Problem is it's not a part I got from Audi. Sourced it from an indy. Maybe I should contact Bosch directly.

[650RS]

Shoppinit - Unplug the maf's and see how it runs and report back, I will help as much as I can

[Shoppinit]

Thanks, guys.

I took it apart again to see if I'd pushed the rubber seals in or something (I hadn't), and decided to try reseating it one more time before putting the old MAFs back on.

Anyway, fired up and ran smoothly. Idle g/s went from 1 to about 3.5 - right in the middle of the range. Took it out and it drove smoothly. All the power is back, no more DTCs. Can't believe what a huge difference a couple of millimeters makes in the positioning of these MAFs. My own fault for not putting the airbox back on properly, though to be fair, it's hardly obvious when it's in place properly.

Let this be a lesson to all. Leaking MAFs cause the DTCs above which are counter intuitive.

The old MAFs were OK, but in the interest of preventive maintenance I'd decided to change the N75 and MAFs. Won't bother doing that again!

The only positive is that the car seems to deliver power slightly smoother under WOT. It's definitely not quicker though. I also accidentally discovered the location of the temp sender. Bonus!

[paul_23]

Shoppinit - if you recall on my thread I changed my MAFs and lower seals and got the same fault codes about lean mixtures for mult and add....
I queried Audi dealer workshop manager who swears he personally fitted them so they are fine but said I need to also change the upper o ring seals too. The O rings are now in stock and I am due to take the car in next week to let them look at it.

Your solution has given my confidence that it is the fitting that is sensitive and it may not be the o rings....what exactly had you done wrong - was it MAFs on badly, or airbox on mafs badly, or o rings not central ........

[Shoppinit]

The rings hadn't budged. They're in there good and firm and I wouldn't really want to mess with them.

I don't really know why I had a problem this time. I've had the airbox off loads of times, and never had an issue. Last night, though, I did feel that the box wasn't going back on as easily as it normally does. I had to wiggle the box to get the screw holes to line up. This morning, it just pushed back into place like it normally does.

I'm convinved that the upper seals won't cause DTCs - at worst you'll be pulling air in throught the MAF that hasn't been filtered.

[mtech114]

Sounds like you havnt put the airbox back on correctly, remove it a refit it ensuring the airmass meters press correctly into the throttle bodies, it's also advisable to replace the seals that the mass meters press into as they shrink with ages! There's a special tool to press them in! I've seen this complaint before! Might be worth checking..? Good luck!

[paul_23]

My car was back at the dealer yesterday for these fault codes and they replaced the upper O ring seals for the MAFS (about 10 quid each) and also a grommet which they said was crushed so one side of the air box was down, causing it not to be level and leak.

I have not checked the fault codes since but it runs much smoother with no hesitation so I think it is cured.....