Thought this might be interesting to share with other 3.0 owners.

Years ago, when I first bought my 03' 3.0, it had a strange random misfire issue that would only be detectable if I got a CEL or viewing in VAG-COM. I took it to an indy shop, and they couldn't figure it out either. You could just turn on channels 14, 15, & 16 and just watch the misfires roll in one by one, but the engine seemed to be running smooth all the time.
I ending up switching from 93 octane to 89 octane and the misfires stopped. I thought this was just a fluke, so I started using 93 again and the misfires would show up every now and then, but not enough to cause a CEL. Have been driving with 93 in my car for years and thinking the misfires on the VAG was due to a bad sensor or something.

Well, I just tried it again, switched back to 89 last week and have been checking the misfires and there are absolutely none. Engine is very smooth. The engine seems less tourqey, but not under powered at all. So it seems the engine likes 89 better than 93. So I guess I've been contributing to an early failure for my CATS. I switched back to 89 because I started noticing carbon on my tips more and more. If anyone else has similar experiences to share, please do.

 

That just screams to me that there must be some weird underlying issue at play, but I'm far from knowledgeable enough to speculate as to what. I've got several ideas, but in lieu of looking like an idiot, I'll let the experts respond...

 

I have a 3.0 Quattro its an 04, I just recently hit a deer, basically totaled the car, blew the bags, but I loved it so much I re-did everything. Well When I hit the deer it broke a piece of plastic off the timing belt cover and wedging into the timing belt itself thus causing the timing to jump and the engine jump time, thus bending valves. Well I had the engine re-built and It has been running Fantastic! The shop did a suprisingly did a great job. Well I have been driving for 2k miles now and my check engine light JUST came on. The shop seamed to think it was a fuel problem the car sat for 2 and a half months so they thought the fuel could have gone bad. (I don't think so) Anyways I have the code 16684 Random cylnder misfire detected. WTF!? I am freakin out about it. Misfires reallY!?!? I will say though the car runs perfect! The only thing I notice is it is a little shakey like the engine is groggy upon cold start ups(it sounds like its misfireing), but only for about 5-10 seconds. Then everything is fine. Does your car have this kind of a start up? I am begining to think its some kind of sensor as well. o2 maybe? The shop put Redline Fuel cleaner octane booster in to see if that would cure the problem but it didn't and the code came right back. Does this at all sound like what your going through? Have you figured out the suloution yet? I am taking my car back to the shop, they re-built the engine so I am holding them responsible to fix this. But who knows maybe there is no realation to them re-building it, if you are having the same type of problem.

 

That's what I said, but it's been like this for years. Wish I knew that was going on. I read another thread about a girl who eventually had to replace the ECM or ECU. This was not the first time I heard of someone having to replace it because of getting misfires. I don't know. Just looking for other experiences at this point. I'll just stick with the 89 at this point.

 

Ya I just saw her post...Read mine on hers about the recall I forgot about that. I was talking to a friend and it reminded me of it. BTW My machanic friend said that putting a lower octane fuel in it just makes your combustion process slower, not just sacraficing performance but definitly not cureing any problems, what the lower octane is doing is basicly creating an illusion that its not happening because its happening slower and you just can't notice it. So I was told, it makes sense. But ultimately you still got the missfire, and what scares me is eventually that missfire can cause damage to other things down the line, you know Audi's and how perfect everything has to be in order for there to be no problems. I am confadent of figuring this out but its just making me nervious.

 

Yea, I read that about the recall. So, is the the misfire really happening or is it a software glitch?

BTW, what is the title of that TSB? I'd like to print it out.

 

Forgive me, what is TSB? And yes the car is actually having a misfire, I can hear it and feel it, but it lasts for only a second or two. No for sure diaganosis yet I have strong suspissions of the ECU (computer) failing, just from other things I have read. This would mean that the computer in the car is actually causing the missfire, the missfire is real and is actually happening but only because the computer is malfunctioning for a few seconds and then fixes itself. This is just a strong suspission, I will for sure let you know as soon as it is confirmed.

 

I have this same problem. Did you ever get this resolved?

 

not yet my car was in the shop all last week and I think they ruled a couple possibilities out like coils and spark plugs I don't know what else yet, but Its back in the shop again this week, I hope they can find the problem very soon.

 

The only thing my Audi tech could think of is the maf sensor. He replaced the coil packs & plugs last summer. The codes show random misfires in different cylinders so its not isolated to just one cylinder. I have the 1.8t btw.