"Rotten" car problems....

[RENIK]

So, out of nowhere this evening, while driving home my car starts running like crap. Driving to work and around at lunch was fine. No indicators of what was to follow a few hours later.

The car can't keep a steady idle. There's a constant revving of the RPMs, about 4 times a second. But only an increase of maybe 100-200 RPMs.
The CEL came on after a minute of this happening and flashes steadily for a few minutes and then will stop for a couple of seconds. Then the CEL resumes flashing again. Sitting at the light in rush hour traffic I get the wonderful smell of rotten eggs.

So I'm thinking the o2 sensor is throwing the CEL because of a bad catalytic converter? The car will make maybe 5lbs of boost, but there is next to no acceleration. I'm guessing the car is running in limp mode?

I'm definitely not the most mechanically oriented person, but I'm hoping I'm diagnosing this correctly. Let me know if this is likely or not. The car just hit 80k miles and is due for an oil change. Probably useless info to post, but who knows...Also, the car is a Tiptronic.

Thanks in advance for the replies.

[rbooth]

COIL PACK! 02 A4's are notorious for having coil pack issues. I had to replace them allllll the time in my 02. VAG-Com your car and find out which ones gone or pick 4 up at your nearest audi dealership and change them all out.

[Raus]

Coil pack needs to be replaced. Please search for it, someone posts the same question at least once a day.

The rotten egg smell is unburnt fuel being dumped in the cat, it will also be glowing red so don't drive it much unless you want to destroy it.

[manguyen]

02 notorious for coil pack problems??? hmmmmm ive had my 02 for 88K miles and ive only had 1 coil pack go.