2009 A3 2.0T TFSI stalling/dying at lower RPM

[logiczero]

Hello,

I recently purchased a 2009 A3 2.0T TFSI with 145K miles on it. It ran fine for a few weeks, but one morning during the commute the car stalled, and it has started doing it more and more frequently since.

Changes I have made to the car: 1) new battery; 2) oil change; 3) disconnected the the Mass Airflow Sensor and drove the car a few times (a suggested method to determine if the sensor was bad), but it still stalled

Symptoms:
The car really seems to have a hard time once it hits 1000-1500 rpm, usually while decelerating. The majority of the stalls seem to happen when the car is decelerating in first gear, such as when slowing down approaching a stop or intersection. It doesn't seem to like engine-braking, i.e. taking my foot off the gas pedal to slow down, but not applying the brake. There have been one or two occasions when I was accelerating, but then suddenly the RPMs would drop despite pumping the gas pedal, and then the engine would die. I've tried all transmissions modes (auto, sport, "manual"/s-tronic), and the car has stalled in all three modes. When it first started happening, the car would start right up after stalling, but the last time it happened a few days ago, it took several minutes of trying to start the car before it would run. The engine would kick over, cough and sputter for a second or two, then die. I did try turning the key and listening for the fuel pump running for a few seconds to build fuel pressure, and that seems to be happening (if I'm listening to the right sound).

Unfortunately, the Check Engine Light does not come on when the stalls happen, and OBDII doesn't show any codes. I had a mechanic inspect the car; he couldn't reproduce the issue, and said bring it back when the CEL came on. Any suggestions would be appreciated. This is my first Audi. I want to like the car, but until I can resolve this, it's basically undriveable...

[evo v]

I had this same symptoms on my first A3 with about 100k miles. It turned out to be carbon buildup. I cleaned it myself. This was my first major job on my Audi. It took me 10 hours to complete. Now I've done it so many times on my cars that I can do it in 2 hours.

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[logiczero]

Thanks for your reply. I assume you mean carbon buildup in the throttle body? I have seen this mentioned elsewhere, and a quick Google search yielded something that sounds very similar to the problems I'm seeing:

"Poor or High Idle
When your throttle body is operating below its normal effectiveness, one of the tell-tale signs is a poor or low idle. This includes stalling after coming to a stop, a low idle after starting, or stalling when the throttle is pressed down rapidly. Dirt causes airflow into the system to be turbulent and leads to a fluctuating idle speed."

https://www.breakerlink.com/blog/mai...eeds-cleaning/

A search on eBay indicates that new throttle bodies aren't all that expensive. Would it be better to just swap in a new one, rather than trying to clean it?

[logiczero]

I now see that GDI carbon build up is a common problem, with various approaches to addressing it. I'll most likely go the chemical route (CRC or Seafoam) and see if that helps.

[tcardio]

Crc or seafoam? Really. Good luck with that


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[evo v]

The throttle body might be dirty too but I am talking about the intake valves. You need to remove the intake manifold.

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[logiczero]

Replying in case this shows up in someone's Google search...

The stalling issues the car was having was due to the engine being a complete disaster, according to a shop specializing in Audis in San Francisco. They estimated it would be $12K just to address the engine issues. I sold the car to be parted out. But here are a few things I learned:

I ran a couple de-carbonization cleaners through the sensor port in the center of the intake manifold. I know that those cleaners are not enough to clean off heavy carbon build up, but I have seen recommendations online that they are useful as a maintenance method if you run them through the engine every 10000 miles or so (to *prevent* buildup). If you have a GDI engine that has been cleaned at some point, and would like to periodically run some carbon cleaner through the engine to prevent build-up, the delivery mechanism from the Berryman's product was way better than anything else I tried: https://www.amazon.com/gp/product/B081TKBG18

Secondly, the mechanic who looked at the car said that the symptoms of carbon buildup usually manifest as rough idling immediately after starting the car (like, you should feel the car shudder while it's idling). My car ran fine for 10-15 minutes before it had issues (again, *multiple* things wrong with my engine, and it may have even had carbon buildup, but it didn't exhibit the typical behavior of carbon buildup, according to the mechanic).

Thirdly, I watched several YouTube videos about removing the intake manifold and cleaning the intake valves. I bought all the tools needed to pull it off and scrape off the carbon, and I started in on doing so. Once I got in there, the thing that was impossible (from my perspective) was removing the bolts on the bracket on the underside of the manifold...I could barely get a fingertip on them, let alone a socket or a torx bit (I'd like to meet the f*cking idiot engineer that thought a blind torx bolt was a good idea). I realized that even if by some miracle I got those bolts out and the manifold off, there was no way in God's Green Earth I was going to be able to get it back together. There simply isn't enough room with all the coolant hoses underneath that thing to have enough room to maneuver hands and tools to get those bolts out. So unless you have a garage where you can tear out most of the components around the front of that engine (which I don't) and have the car sit for a week or two while you do it, the YouTube videos are...shall we say...a little overly optimistic. Unless you're under the age of 30, three hours of leaning over an engine is exhausting, and you won't be doing it multiple days in a row.

The mechanics told me that there were at least 6 different reasons for why the intake manifold could be removed, and someone had clearly been in there before me, because two of the ten torx bolts holding the manifold on were replaced with hex-head bolts (one 8mm, the other 10mm). I got it off Craigslist, and someone screwed me over, and yeah, I should have known better, but pulling off the intake manifold and cleaning out the carbon is well beyond intermediate mechanic skills.

This obviously shouldn't reflect negatively on Audi. The car seemed like it would have been fun, I was just unlucky. But it is NOT a car for someone without a serious garage and fairly advanced mechanic abilities.

[Silicon Voodoo]

You weren't unlucky, this is the typical state of things for Audi this age.

I sold the car to be parted out

The only reasonable thing to do with an Audi.

[evo v]

The first time I did carbon buildup cleaning I was intimidated and scared. It took me 10hours over two days weekend. I did it in my friends garage where I can use all his tools.

I've done probably 10 cleanings since then. I'm done to 2.5 hours on my driveway. It's not for everyone but once you know how to do it it's not that bad.

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