Audi Mystery


I have a 1999 Audi A4 Quatro with 150,000 miles. A few months ago it started missing randomly. There seems to be no correlation to misfires. A computer diagnostic indicated that cylinders 1,2 & 3 were indeed missing. My mechanic - who works on a wide range of foreign cars - has tried everything he can think of including swapping out the computer, new plugs, new wires, new fuel filter, new vacuum something or other. He even had the local Audi service manager look at it - and he was stumped. Before I sell it for parts does anyone have an idea as to what would cause the problem?


Coil? Have you tested the fuel pressure? Original injectors?

While thinking this over let me ask this. (This a V-6 I assume?)

In regards to the missing cylinders are they all 3 missing all of the time, meaning this car will barely run or even move itself or are they missing somewhat; meaning that those cylinders are at least firing erratically and the car will drive at speed although it may be running a bit ragged?

If it’s a 1.8T the ICM may be failing .

It’s an A4 Turbo - 4 cylinders. As I said it misfires, meaning it erratically. And as I said it happen randomly, not all the time, sometimes it runs perfectly.

Coils are being checked today (at your suggestion). Fuel pressure is up to spec. Injectors were cleaned then replaced with new ones.


ICM was replaced.

I don’t know much about Audis, but I remember Audi and Volkswagon had problems with their coils somewhere around this era.

Try PassatWorld - lots of good info there .

Any update?

We have tried everything suggested. It still misfires. It they can’t fix it within a week or two I am going to sell it for parts.

I wonder if the knock sensor is failing?
Maybe its randomly throwing out signals that causes the ECU to retard the timing, that then makes you think its missing…


Does it have a distributor cap? if so try replacing that. Otherwise ignition coil pac

Don’t give up yet (if the rest of the car is in good shape.) There’s a finite number of things that could cause this & it’s probably not too expensive. Keep researching the internet, ask a different mechanic, have the Audi dealer call their technical help people.

I have a 2002 a4 3.0 V6 with the same exact problem. random misfire. it’s more prominent now and it is running extremely rough and the vibration is killing me and my manual transmission. Seems like it all started after I had the coilpacks replaced under warranty. I’m hesitating to have the gremlin investigated because I have read other tales about changing parts with no success. There is NO CEL. When the dealer hooks it up to the computer, no major malfunction is detected other than the misfires on cyclinders on both sides of the engine block, but the misfires are not consistent. I’m at my whit’s end, and I’m fearing a never ending story. Any success on your end?

It’s no mystery…It’s an old AUDI.