Strange intermittent stumble

[jesus_man]

It seems my problem surfaced after I installed the P2015 Code Repair Bracket from dieselgeek. But we've also moved to a new climate and driving style has changed a bit due to driving in different neighborhoods.

As I am cruising out of my neighborhood with 15, 20 & 30mph speed limits the car will hesitate, stumble briefly, or change speeds give or take a mph or two. It doesn't seem to die out, but it's just enough to feel the car lose power and slow before it goes back to normal. There are times I can get it to do this for 10-15 seconds if I hold the same speed. It smooths out if I accelerate or lift off the throttle. It also seems to correct itself if the transmission shifts to the next higher gear.

Oddly enough, I just performed my second DSG fluid change a few weeks ago and the problem seemed to have gotten better and the transmission behaved better. But the car seems to have gone back to it's old ways. Let me explain this behavior as I fear they may be related. The transmission seems to have a lot of slack between stop and go. I've adjusted my driving style to accommodate it, but if I come to a stop and then go, I have to ease into the power or the car will jolt to moving forward. The same thing happens if I am coasting and then accelerate. It's almost as if the CV half shafts can turn 180* before they catch. I have checked my CVs and they are fine, but if you imagine the feeling that would cause...

Here's my theory and I hope you can prove me wrong. I am afraid the transmission is on it's way out and the stumble I feel is the transmission wanting to shift gears, so it sends it's signal to the engine, but then redacts that request and stays in the same gear. Meanwhile the engine cuts power to prepare for said shift, which then didn't happen so it resumes.

Another odd engine stumble happened yesterday at 70mph, which it's never done. Happened twice on the same commute, but hasn't happened since. And in fact, the car today runs and shifts like a car with 145k should.

I am not getting any codes. I have run the ross-tech report, but I didn't get a chance to look thru it in detail. I am confident it is not water in the intercooler as I have a drain valve hooked up to that which is very slightly open and drains each time the turbo creates boost.

So what else? Could it be that the valve the dieselgeek bracket is on is hunting for a happy spot and it can't get back to where it was used to going?

Thanks for the help! I want to get a Malone Stage 0.5, but I can't justify it with the car doing what it is right now.

 

[tjg]

Is it anything like in this thread? There's some videos that replicate what you're describing:

2013 A3 CBEA engine stutter

So I recently picked up a 2013 A3 TDI. Occasionally, on cold starts, it will get a flat spot or stutter (I'm pretty sure always in 2nd gear) that goes away after a few seconds. It doesn't happen all the time so I chalked it up to residual moisture in the intercooler/intake, but now that we're...

forums.tdiclub.com

 

[jesus_man]

It's hard to tell really. Mine doesn't hesitate when accelerating. It's more just idling along with dead spots, but only when I am driving. It doesn't just idle in the driveway much, but I've never had s stumble while stationary since I fixed water in the intercooler issue.

I do like the idea of the issue being EGR tho...

 

[prsa01]

Update - Post 10 in this thread has links to the threads I'm thinking of :

Hesitation/stutter while driving

Having an odd issue that I’m looking to try and track down. First: there are no check engine lights While driving when first started during the day, OCCASIONALLY I will have stuttering like a cylinder is missing (I compare it to having a coil pack failure on my golf r). Doesn’t happen again...

forums.tdiclub.com

I can't find the thread(s) right now and I'm not sure if this matches your symptoms or not but there are multiple threads about a common issue with stumble/jerking/surging at very low power input (just barely touching the peddle).

Iirc consensus was that the computer can't decide whether to fuel or not. AFAIK there is no solution. This, and the long first start of the day are the most annoying, apparently unsolvable (without tune) , issues with my car.

 

[tjg]

So I was told by Audi, after the dealership reached out to the AoA level techs, that that stumble is normal and due to the exhaust valve opening/closing in order to maintain proper emissions levels.

 

[jesus_man]

Thanks for the info. It does seem similar to what everyone has described. What is odd is the car didn't always do this that I noticed.

Either way, if some tuning helps, then I am headed down that road anyway!!

 

[Wilkins]

My experience with exhaust valve stumbles is that they get worse with time once they start happening. First couple of years I had the car no stumbles, then progressively worse until the valve seized wide open. I drove like that for about a year, car ran great. No stumbles, better economy, just a CEL to ignore.
The fix installed a new valve and no stumbles for about two years, just started again recently.
If you have VCDS or Polar you could see if the stumbles coincide with the regen status changing from 01 to 10 and vice versa- that would confirm exhaust valve related. Otherwise unplug the valve and see if they go away. Some people have had problems from the valve not working so I’m not sure you should leave it that way for long but it should be fine for a diagnostic test.

 

[jesus_man]

I have VCDS, but wouldn't have a clue on how to monitor and it's still pretty irregular. But perhaps I can figure out where to unplug it and see if it goes away next time.