CurtisPlug

Hey all,

I bought a Q5 3.2 with 140,000 km (approx. 90k miles). I immediately took it on a 1200km trip home, where it drove perfectly (other than the MMI, but I've bypassed the amp for now and its good). I put on probably another 1000km before taking it on another 1200km trip (each way). A few hours into the drive back, I thought I felt misfires on acceleration, but was not sure, could just be bumps in the road. It got progressively worse until 200km from home I went to pass a semi and the misfires were so bad I barely got past him due to no power. As I got past, the car started shaking violently, and the EPC light came on (don't remember if it was flashing). I immediately pulled over and turned the car off. But I had to get home so after 10 minutes I turned it back on. The EPC light was gone and car ran smooth. I babied it ever so carefully home gaining all my speed down hills and losing all of it up hills. This way, I did not feel any misfires. Chucked a cheap code reader on it once I got home and some P03xx codes came up. Misfires on cylinders 2,3,6. Maybe foolishly, I cleared the codes to see if they came back. Driving around town after that, I felt no misfires. I also ran a fuel injector cleaner through the gas tank. I even took it on an approx. 1hr drive a few times to try make it come back. Thought maybe I got lucky and clearing the codes fixed it (maybe reset fuel trims or something). A few months later it was time to drive back to university, 1200km. Again, a few hours in the misfires started coming back. Stopped at a euro mechanic in a city to see if they could find anything, and they said no codes whatsoever relating to the drivetrain came up. They had no idea. So my only choice was to keep driving. I babied that car so much that a 11 hour drive turned into a 15 hour drive. Misfires got worse and worse, I think worse than the first time they came up.

Ive read through many forums and it seems that misfires are often coils, but it seems to also be that people end up throwing thousands trying to chase down the problem. I'm a full-time student, I cannot afford to do that. This only happens with long drives though, that must mean something. If it means anything, I feel that my oil consumption is much much worse on the highway as well. I've never had to add oil while driving city, but have had to add oil on each long trip (except the first). Could this be relevant? Could it be something to do with heat soak? I'm stumped.

Things I have done:
Pulled spark plugs - look fine to me. Only one had the white residue on it.
There was a bit of oil on one or two of the coils, so valve cover gasket could probably use replacing. Could this be messing up coils?
Checked for carbon buildup - I thought it was quite a bit, sent a pic to a mechanic friend and he said it wasn't enough to be causing my symptoms. Also seems to be weird that carbon buildup would only cause misfires on long drives.

tomaszp72

Based on what you are describing it could be related to injectors. Bad gas, dirty injectors or bad injectors. Try to run 2 bottles of tectron injector cleaner on a half empty tank of gas and see if this helps. I used to have a 2.8 V6 passat with a very similar problem.

CurtisPlug

I’ll give that a shot, thanks. Seems odd that it just happens on long drives, also makes it difficult to test any potential fixes

AudiFahren11

Sorry to hear about your troubles. I have a 3.2 from 2011 with 175k miles on it and it runs well, but throws a rich code every once in a while which I believe is a leaky injector.

Did you get a code mentioning rich or lean condition? Or just the misfires?

It is most likely plugs and coils if you are not getting rich / lean condition code.

Also replace that valve cover gasket or it will chew through motor oil like a Volkswagen. ; )

turbo510

I'd change the coils. Your long drives keep them hot long enough for the weak ones to quit. It's happened on our 3.2. The shaking you felt was the cylinder-disable kicking in, shutting off the fuel to the affected cylinder(s). A whole set of six is a bit over $100 at autohausaz.com for Bremi OEM coils ($17.69 each). Personally, I'd change the plugs too while they were easy to reach.

CurtisPlug

Thanks for the suggestions. Turbo, you had the same kind of thing happen? Was it also just on the longer drives? AudiFahren, no there were no rich or lean condition codes. Haha yes it is definitely going through a bit of oil, I'll get that done soon. I'll probably do coils and plugs, fairly cheap to try out.

turbo510

The first time that it happened, we had just driven from Phoenix AZ and were within 10 miles of home when it did that. I pulled over with the engine shaking, shut it off and re-started. This began to occur more often, so I bought one coil from the Audi dealer and installed at the problem cylinder. Some time later, another began to be unreliable, so at that point I just installed a whole set of six. My son now has the Q5 (my wife bought an '18 Q5 2.0) and has had no coil problems.

Ct4funf

Changed coils and plugs still get the C2M
Unless it's a specific injector I can't figure out why it'd only be that 1 #2 cylinder.
When I clear the code she runs great misses at idle but then is running on all 6. Sometimes the CEL will stay off for over 125 miles. Sometimes it'll come on in 2 miles or at start up.
I'm completely baffled

m1964

Had the same problem on 2010 Q5 with over 100K miles- you'd need to remove the spark plug and check with a camera for a leaky injector.

Ct4funf

did you ever get an EPC light?
That's new. The C2M triggers the CEL & has been going on for a while and kills the power but the EPC is new & IT doesn't throw a code. Car runs fine with it on tho....it just limits it to 4k rpm