matthew1874

I just purchased a 2012 Audi A4 2.0T with 97k miles on it. I purchased it from an Audi dealership. As soon as I drove it home, I noticed a very specific problem: Upon medium or slightly heavy acceleration, at 2800 to 3100 RPM's I experience a very brief "miss" or loss of power, and I can feel it. I can also see the tac drop very slightly for a moment. It is only at that RPM, and does it consistently. There are no codes. There are no other problems. Under slow or less acceleration, it is not noticealble at all. I took it back to the dealership and they kept it for several days, ran tests, and could not find out the problem. They pulled some fluid, sent photos to Audi tech, and they advised the fluid looked "normal". The dealer finally said they unplugged the Mass Air Sensor, and let me drive it, and it seemed to not do it, while the sensor was not connected. So they replaced the mass air flow sensor. I just got it back yesterday, and it's doing exactly the same thing. The dealer said they are completely stumped. The shop forman told me he thinks its transmission related, but they have no codes, and the transmission isn't missing or banging. He still thinks its transmission related, but they have nothing else to go on, and will not "throw parts" at it. I was sent home and told "drive it until something breaks". Well, I'd rather not do that, and was wondering if anyone has an answer for me! Any help is appreciated. It's got the dealership totally stumped, and makes me think i'm crazy, but they rode with me, and i showed them and they even took a video of it, but said they just don't know what the problem is. There has to be an answer. Please help! Thanks!! (I hope I'm posting in this correctly, I am brand new to Audi and this forum!)

matthew1874

According to Audi, there was a service bulletin that said the MAF in that model sometimes would fail, but not produce codes. They replaced it, but it did NOT fix the problem. They have absolutely no idea what the problem is. Anyone have any suggestions what to tell the dealer to get to the bottom of this?? It's very noticeable when I'm accelerating at medium load, which is awful! Thanks!

zbillz

I have been experiencing the same 'phenomena' just as you describe in my 2011 Q5 for several months. My local dealership also provided similar feedback (almost verbatim), saying it is likely transmission related but since there are no codes they cannot pinpoint the exact cause.

I replaced the MAF (no change), checked for vacuum and boost leaks (found none), and the next thing I am going to try is changing the transmission fluid and filter to see if it could be an issue with Audi's 'lifetime' fluid. Because the issue is RPM and load dependent, the other potential cause I am researching is a worn cam follower on the high pressure fuel pump (HPFP). My theory is that if the cam follower is worn, it's contact with the camshaft at higher RPM's may be compromised, therefore screwing with fuel being delivered through the HPFP, leading to the sensation of a slight miss in that RPM range. The counter argument is that this should throw a code, but it may just be out of the 'normal operating range' of the senors - enough effect to the feel (hesitation/lurching/"slight miss") but not enough to trigger a fault code.

The more you drive your car, the more you might notice that the performance and smoothness of the engine above 4,000rpm is also 'slightly missing', adding to the HPFP issue theory.

This is where I'm at. Hoping someone with much more technical knowledge than me can help us out.

jagtoes

Get your money back. return the car.

matthew1874

how in the world would I get that accomplished? Just tell them I want to return the car?

jagtoes

Check with a lawyer. Some states have 30 day return laws or misrepresented sales. Talk to the dealer and tell them you want your money back as they sold you a defective car and they knew it.

Caelismadison

I wonder what would happen if you unplugged the avs solenoids so the exhaust cam couldn’t make adjustments. And I’d also like to see what would happen if you unplug the solenoid for the intake cam adjustment on the upper timing cover. It’s odd that unplugging the MAF makes it stop but replacement didn’t fix it.

SMac770

If one knew what thoroughly changed with the engine management when lacking MAF input, it might be more clear. It could also be that the different maps that are used when lacking MAF mask the actual problem, which lies elsewhere. Or it could be a harness issue and the lack of electrical connectivity on those lines is not causing interference or problems on adjacent lines.

Not sure why the tranny would be involved. If it's under acceleration, I assume it's not shifting gears. And I doubt the acceleration started from cruising at 2800rpm. 3k says exhaust cam actuators to me; only thing I know that events around 3k rpm. But maybe intake cam adjustment profile changes over at that point. Or maybe that's a change point in throttle maps and fuel trim. Who the f knows.