Hi All,

First post - but unfortunately, it's because of a problem. Been reading and learning a lot about the B5!

I have a '99.5 A4 Q with auto and 138K and the AEB motor.

The car drives fantastic and gets great MPG. However, in the past few days, I have been experiencing a strange bogging problem.

The car will start and drive fine, then out of nowhere, the car will start to bog at lower RPMs (0-3200) ** at this point if I start to accelerate, the car will be jerky and I can't get past 3K rpm. But if punch the throttle and leave at at the upper RPMs, I can sort of maintain speed/boost, but I can still feel the bogging.

Once back at idle - the idle will be very erratic and will almost stall itself out.

The strange thing is: if I shut the car off, and restart it, the symptoms will ALL go away, and the car will drive/behave like normal. The car will drive fine for the rest of the day, until the next day when the problem may or may not appear. At no point does the CEL light come on.

First thing I did was check the coils, and it looks like I have one replaced coil from the previous owner. The rest were the 'S4' labeled ones. I have not yet replaced the coils as they are expensive ($90) each on the AEB motor, and from what I read, they rarely go bad.

I also replaced the ICM with a brand new Huco unit with the same results. The previous owner had a Huco unit on there as well.

The motor does not sound like it's misfiring as the CEL never gets triggered, but rather starvation of gas or something like that. I asked a mechanic about the fuel filter, but it's located inside the tank and not easy to replace.

Any ideas on what to check next? If I get a VAG COM unit, can I read failures, even though the CEL is not triggered?

Did I get a bad tank of gas?

Thanks in advance!

 

sounds like a MAF issue to me

 

VAG COM will allow you to read any fault codes if the ECU has stored them. It's likely that it has in this case. VAG COM is a good investment in general anyways.

 

After reading a ton, I agree with you.

I cleaned the MAF yesterday and the problem has not appeared since. I'll keep my fingers crossed though..

I guess now I have a spare ICM!

 

Well, after 1 day of no failure, the bogging came back today when I was driving home from work. So either I didn't clean the MAF completely - which is possible since I did not remove the MAF (it's in the airbox) or it's something else.

 

Vag Com readings:

Address 01:
2 Faults Found:
18010 - Power Supply Terminal 30: Voltage too Low
P1602 - 35-10 - - - Intermittent
17963 - Charge Pressure: Maximum Limit Exceeded
P1555 - 35-10 - - - Intermittent

Address 02:
2 Faults Found:
00518 - Throttle Position Sensor (G69)
27-10 - Implausible Signal - Intermittent
00526 - Brake Light Switch-F
27-10 - Implausible Signal

--

Anyone can interpret about voltage? And overboost?

 

The same exact thing has been happening to me for about a month now. It only happens after I floor leading me to believe it's overboosting then the ecu is cutting fuel to protect the car.

 

I have been reading like a mad man, and it looks like the MAF is the culprit.

As for the other codes, Power supply terminal is because I had recently unplugged the battery, and the brake light switch is normal on auto transmissions.

I still don't understand the TPS code on the transmission, so i'll dig into that after I replace the MAF.

 

In theory that is exactly the correct behavior.

But what is causing the over boost to be triggered? I can certainly see a vacuum leak or bad N75 valve, but in my case since it occurs occasionally, it makes me think the fuel calculation is wrong, or fuel pressure.

I did manage to get the car to not fail for 2 days after a good MAF cleaning, but I don't think that will be enough.. I think it needs to be replaced.

And for those that will say to unplug the MAF, the AEB motor will not run with the MAF unplugged!

 

For the sake of closure, the problem was the MAF. I bought a new one and all is well!