2000 A6 2.7t, 150,000. My idle is not as smooth as it should be. My brain says, "weak cylinder". It's not really bad but at idle, and only idle, the car slightly shakes side to side in time with the engine speed. I think that I can feel it a little bit in the midrange at light boost too. There is no loss in power or fuel economy, which have gotten better since the temps have dropped here in Michigan. I just had a power output stage go out recently, so I know what a dead cylinder feels like. Happens with no difference between engine temps and no CEL yet.

I was thinking of starting with the fuel filter, then injectors and so on. Spark plugs replaced recently as I just started to feel the problem. None of them looked abnormal. If there is such a thing as a weak ignition coil, is there a way to find it?

Thanks for the help.

 

log measuring blocks for misfires, I believe they are 15, 16, 17. Find what cylinder is missing most often, swap the coil pack from that cylinder to the one with the least misses. Re Log, see if the miss jumped cylinders, if it did, you have a weak coil pack

 

Measuring blocks? Again, no misfire codes. No CEL.

 

Vag Com, open engine contoller, go to measuring blocks, select fields to be logged, just because you have no misfire cel or code, does not mean that it isn't misfiring. I believe in order to trigger a cel a single cylinder must miss 3 times consecutively. Using Vag Com, you can get a real time misfire count from all the cylinders

 

My 03 has 153k and I think it is running a little rougher than when I got it with 37k miles, but no CELs (and no vagcom). But I last did my plugs at 107k and they may be due again. I'm amazed that your mpg improved with MI's colder weather. I drive to Detroit weekly and notice a 2-3 mpg difference in gas mileage now that the temp is in the 40s vs this fall when it was in the 70-80s.

 

If you are using sidefire or platinum plugs, they are due now, If you have copper plugs in, they are wayyyyyy over due