Hi everybody,

I really need somebody who can help me out with this crazy problem and I appreciate any answers I can get.

I hope you really are proud problem solvers becuase Ive been spending every waking hour thinking about this problem and I just cant solve it.

I bought my Audi A4 B5 AVV 2 years ago for a great price. It was in good condition when i bought it except it had an engine light p1137 but i figured that shouldnt be a problem to fix it after i made some google searchin. After 2 years of being intermittently home and away im now permanently home and wanted to finally make an attempt to fix this long going problem.

So heres my case.

When I bought the car the previous owner told me that sometimes the brake pedal sinks after a long braking action and when it does so, the braking gets kind of abrupt.
Scenario: if im slowing in for a red light 100m or so before.. slowly and gently i brake at a fixed pedal angle then randomly the pedal sinks down like if something is grabbing it from behind and pulls it down to the floor(like a suction) and the car gets kind of jerky and quick stopped. So i figured, it has braking power so no air in the brake lines? I dont know.

At the same time when I have stopped at the red light and released my foot OFF the brake pedal, I can hear from the engine bay a weird noise for half a second. I had a friend leaning over the bay with open hood and he pointed out the noise. I can describe the sound like when the door locking mechanism opens and locks the doors like if you make a base sound with your throat "MMMM". It was coming from the ABS module area but hard to pick the exact spot.

I googled the "P1137- P0172 - Fuel trim; Bank 1: System too rich" problem and some articles put me to believe it was a faulty or clogged suction jet pump because somewhere i read it was a common problem.



Yep that was clogged so replaced it with original part. I was thinking that maybe this bad boy had something to do with the vacuum help for the braking action and hopefully this was fixed now aswell. So -Reset engine light. In the same wave i tried to understand WHY it had been clogged so I was just scouring the pipes and lines and discovered a the big rubber pipe after the MAF sensor was broken in the spring parts so maybe some particles and debris came in that way. perfect. replaced that.




So what now? Problem solved with the P code? did it perhaps fix vacuum leaks for the brake servo?

No after some 30km it came back. What the heck.

So I plugged in my VCDS and checked if the lambda sensors values could give me a plonk in the right direction. The fuel trim at IDLE was showing -9.9% and the elevated engine speeds +3% or something so I read on about that. That could indicate "Add" means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter. The malfunction (e.g. vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.

I also checked the peak value when throttling down on 2nd gear. the MAF read around 60 g/s of air at 4-5000 RPM. Ive read that a correct MAF reading should be 80% of your total HP(which is 100 of my 125HP). I didnt want to go all the way to the red becuase it was after a cold start(-4 degrees this morning)- should i peddle down and touch the red?.

So vacuum leak. Whats the step now? Shall i go and get a smoke machine from the nearest club and se if theres leaks in the system? Will the ONE solution fix both the P-code and the braking weirdness perhaps?


Is the ABS module faulty? - strange MMMM sound
Vacuum leaks in the system? - P codes and brake fix?
Bad MAF sensor? - P code fix?
Bad brake servo? - Brakes fix?

Any Einsteins here who can point me in the right direction?

I really appreciate any answers I can get.

Kind regards,

Christian

 

On your p1137, 'system too rich' - it could be your MAF sensor..have you cleaned it really well? a quick test for the MAF, with your car running, unplug the MAF, if there's NO difference at all, it indicates a bad MAF, if it's good, the car should idle worse.....You can use special MAF cleaner or a substitute. Since you found 'debris' in the pipe that goes to the MAF, check the MAF filament to see if it's broken. If it's broken, time for a new one....otherwise, clean it really well and see if it fixed it, but with the debris you found in the pipe, I would definitely check it.

Could also be a vacuum leak, but you checked it pretty well.

Since you have a VAG COM, and NO faults on the ABS system, see if the VAG will communicate with the ABS Module, if it CAN'T communicate AT ALL with your module, the module is shot and you can have it rebuilt or buy a new one ($$$$)....

 

I will definitely clean it properly with electric cleaner and see if the problem sustains. Otherwise i found a new MAF sensor for 40 euros incl shipping. Audi charges 250 euros with my old MAF in return hah. bastards.

The thing is with the the engine, I DONT feel its actually running ROUGH at idle or at all.
It sounds quite normal to me. Do you mean unplug the sensor to the MAF or the whole unit to compare the engine sound?


My ABS Module IS responding properly with me via VCDS so I reckon this guy is good.

I was gonna bleed my brakes today but the air nipple had rusted itself shitless so I had to go and get new nipples for the front and tear the old nipples apart but carefully. I will bleed later this week since im off from wednesday.

I will also go and get a smoke machine and really go through it thoroughly so there is no small gaps that the eye easily can miss and the ear cannot pick up.

Thanks for your opinion markymarc.

 

Yes, while your car is running and ideling, unplug the MAF and see what happens. On my 98 when I umplug my MAF while ideling, my car stalls, others it will just re-learn quickly but idle rough as hell....depends on your car, but if you unplug it while it's ideling, wait a few, if nothing changes, chances are the MAF is bad...