Hi. My Audi:

2005.5 Audi A4 Quattro Turbo B7 - 215/55R16 2.0L L4 DOHC - 130K miles

I bought this recently. Its in great shape and I love the car. But I do hear an engine surge around 25 to 40 MPH. The sound is low frequency and the car speeds and slows just a little bit. If I give it a tad more gas it goes away. The owner of the Audi/VW shop where I bought it says he has the same issue and can't diagnose it himself. And they are quite expert. He took it to the local Audi dealer's service center and they did not have an answer either.

Has anyone heard of this? It is not a beg deal but I'm hoping that it is not a sign of greater problems.

Thanks,


David

 

Forgot to mention there are no codes.

 

Today I was driving my daughters 2006 a8L 4.2. I was on a us hwy, going about 60, when all the sudden the car took off. Gas pedal was not pushed down by me but I felt it go down.The floor mat was not caught under the pedal. It happened while at speed, in the rain. I had to shut off engine w/ key, shift into neutral.. drift to side of road. Before I came to complete stop I restarted engine. Jumped up to 5k rpm instantly and was climbing, so again I shut off. It was still in neutral so I had to act quick fearing the high rev would blow the engine.

​​​​ Coasted to stop. Turned on emergency flashers, opened door and hood, checked the mat which was still on the guides, knowing there was no cable and it's fully electronic I couldn't make sense of the issue. My only though was, knowing the fuse boxes on both sides of dash sometimes collect moisture etc. That maybe a water drop shorted something. I checked all fuel and speed related fuses all good, didn't see much moisture but some was present.
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​​​ While I do not know the exact blueprint of the system, I do have the jest in my head, and could figure out no other conclusions that made any sense. The cruise control on the car is currently out. Hasn't worked since she got the car, and I haven't replaced the relay that I believe is responsible for it's function or even verified it was the relay or the control unit or switch etc. Basically I have not attempted to chase the issue down as she mostly drives in town.

To me It felt like the launch function. I obviously didn't have my foot on both orders and was not at a stop. I realized that this had happened to me 1 other times. It was at a light. I was stopped, when it turned green, I pushed accelerator with with same foot I had applied to break, as I'm not a 2 foot driver. I learned on a 3 on the column, so I learned with the only foot ever on gas or break is my right foot. I assumed somehow the launch function was this culprit. Also this time it initially slowed some with breaks pushed, I was able to turn into a parking lot and it stopped while car was running. I'm pretty sure it was not raining on this day.

My daughter was in the rear seat with her baby today, and she told me that it had also happened to her 1 time, and her only option was turning car off and stopping. It was fine on restart for her. While I love the car, and it is safe for her and baby by quality standards etc This malfunction makes me total rethink the safety of the vehicle as in some situations it could turn deadly. How can I trust a car that seems to at random points take off at full throttle and not respond to anything as far as removing all pressure from pedal, or hitting brakes?

When I was going 60 and it started, brakes were useless.With these 3 incidents, that have all 3 happened in the last 2 months, and only finding threads like this one and no one seeming to have any idea accept human error I don't think I could figure out the issue myself and honestly do not have the time to attempt to. I would like to know why this happened, but I no longer trust the car at all, and it will be sold. I love the car but I can't have this issue continue for me or anyone. I will notify the new owner of the incidents, but I really don't have time or patients to go to dealer with a 18 year old car and be told it was human error when I know 100% it was not. There was absolutely no mat holding the accelerator pedal. It was not the accelerate button for cruise as it's inoperable. So obviously something has to cause this. Even with the previously mentioned safety measures in place. They did not stop the car from accelerating. They did not shut off the engine. Had I not turned off the car with the key, it would have blown the engine I'm sure. I know it's hard to believe with all the safety features in place to stop this from occuring, but it happened.

I hope someone finds the answer, and fixes the issue. While it's obviously not common, it does happen. While I am not a mechanical engineer, I have a fairly high amount of knowledge on cars and have been doing mechanical work on them for 32 years on my own cars. I have built cars from the ground up. I have built several engines, etc. I do not consider myself an expert on Audi by any means, but I do know that it was not caused by human error, on 3 separate occasions, in 3 different situations, by 2 different people in the same vehicle.

I can understand how some will say it had to be floor mat stuck since they are easily dislodged. I have overcame this by putting Velcro under the front mats since she bought the car. Every time I would open the door the mat would be dislodged. So I fixed that issue long before any of this. On a side note, just so if it may be connected some way, the mmi is currently been off. It was off when purchased due to clogged sunroof drains that were fixed right off. I just haven't gotten the new board yet, after tracing the issue to be the board. Anyway I don't think it would have any effect on this but who knows.

 

​​​ While I do not know the exact blueprint of the system, I do have the jest in my head, and could figure out no other conclusions that made any sense. The cruise control on the car is currently out. Hasn't worked since she got the car, and I haven't replaced the relay that I believe is responsible for it's function or even verified it was the relay or the control unit or switch etc. Basically I have not attempted to chase the issue down as she mostly drives in town.